Update Podfile documentation for RN >= 0.42.0
Update Podfile documentation for RN >= 0.42.0

Summary:
I've updated the documentation that gives an example of Podfile adding a note that from React Native 0.42.0, users have to explicitly include Yoga in their Podfile.

I didn't want to modify existing `Podfile` from this documentation because they refer to `Podfile` from existing projects that do not use RN 0.42.0. So I just added a note and an example to explain how to include Yoga.

This PR is to fix the following issue: https://github.com/facebook/react-native/issues/12670
Closes https://github.com/facebook/react-native/pull/12728

Differential Revision: D4716172

Pulled By: hramos

fbshipit-source-id: 12a6e61b0d426c776a7cc2dea3ac22a50ffe56ef

rickbeerendonk/react-native,shrutic123/react-native,janicduplessis/react-native,Livyli/react-native,doochik/react-native,doochik/react-native,kesha-antonov/react-native,facebook/react-native,exponentjs/react-native,negativetwelve/react-native,happypancake/react-native,exponent/react-native,formatlos/react-native,tszajna0/react-native,Swaagie/react-native,Swaagie/react-native,adamjmcgrath/react-native,pandiaraj44/react-native,exponentjs/react-native,farazs/react-native,arthuralee/react-native,shrutic123/react-native,brentvatne/react-native,formatlos/react-native,facebook/react-native,aljs/react-native,janicduplessis/react-native,happypancake/react-native,ptmt/react-native-macos,cpunion/react-native,clozr/react-native,javache/react-native,myntra/react-native,facebook/react-native,brentvatne/react-native,lprhodes/react-native,thotegowda/react-native,Ehesp/react-native,frantic/react-native,forcedotcom/react-native,Ehesp/react-native,alin23/react-native,PlexChat/react-native,PlexChat/react-native,aljs/react-native,peterp/react-native,Maxwell2022/react-native,jasonnoahchoi/react-native,myntra/react-native,Guardiannw/react-native,Guardiannw/react-native,ndejesus1227/react-native,Guardiannw/react-native,happypancake/react-native,pandiaraj44/react-native,dikaiosune/react-native,Guardiannw/react-native,exponentjs/react-native,forcedotcom/react-native,mironiasty/react-native,happypancake/react-native,shrutic123/react-native,hoastoolshop/react-native,Livyli/react-native,chnfeeeeeef/react-native,clozr/react-native,exponentjs/react-native,Guardiannw/react-native,alin23/react-native,frantic/react-native,ptomasroos/react-native,doochik/react-native,brentvatne/react-native,dikaiosune/react-native,peterp/react-native,pandiaraj44/react-native,mironiasty/react-native,frantic/react-native,Guardiannw/react-native,brentvatne/react-native,farazs/react-native,imDangerous/react-native,javache/react-native,peterp/react-native,Swaagie/react-native,ptmt/react-native-macos,tsjing/react-native,Swaagie/react-native,adamjmcgrath/react-native,jevakallio/react-native,javache/react-native,hoangpham95/react-native,forcedotcom/react-native,csatf/react-native,ptomasroos/react-native,alin23/react-native,happypancake/react-native,mironiasty/react-native,myntra/react-native,thotegowda/react-native,ndejesus1227/react-native,arthuralee/react-native,makadaw/react-native,facebook/react-native,thotegowda/react-native,doochik/react-native,hammerandchisel/react-native,hoangpham95/react-native,Bhullnatik/react-native,gilesvangruisen/react-native,csatf/react-native,lprhodes/react-native,orenklein/react-native,farazs/react-native,arthuralee/react-native,mironiasty/react-native,tszajna0/react-native,makadaw/react-native,adamjmcgrath/react-native,cdlewis/react-native,Bhullnatik/react-native,Maxwell2022/react-native,Ehesp/react-native,forcedotcom/react-native,PlexChat/react-native,Maxwell2022/react-native,Ehesp/react-native,myntra/react-native,doochik/react-native,Maxwell2022/react-native,rickbeerendonk/react-native,skevy/react-native,Livyli/react-native,hoangpham95/react-native,exponent/react-native,forcedotcom/react-native,peterp/react-native,gilesvangruisen/react-native,Bhullnatik/react-native,ptmt/react-native-macos,javache/react-native,hoastoolshop/react-native,hammerandchisel/react-native,peterp/react-native,farazs/react-native,adamjmcgrath/react-native,arthuralee/react-native,clozr/react-native,makadaw/react-native,tsjing/react-native,Ehesp/react-native,hammerandchisel/react-native,lprhodes/react-native,skevy/react-native,PlexChat/react-native,lprhodes/react-native,orenklein/react-native,cdlewis/react-native,hammerandchisel/react-native,hoastoolshop/react-native,hoangpham95/react-native,skevy/react-native,facebook/react-native,kesha-antonov/react-native,jasonnoahchoi/react-native,makadaw/react-native,hoangpham95/react-native,farazs/react-native,dikaiosune/react-native,forcedotcom/react-native,Guardiannw/react-native,Swaagie/react-native,ptomasroos/react-native,thotegowda/react-native,lprhodes/react-native,dikaiosune/react-native,lprhodes/react-native,orenklein/react-native,alin23/react-native,mironiasty/react-native,thotegowda/react-native,jevakallio/react-native,chnfeeeeeef/react-native,orenklein/react-native,skevy/react-native,myntra/react-native,gilesvangruisen/react-native,clozr/react-native,makadaw/react-native,cdlewis/react-native,PlexChat/react-native,facebook/react-native,cdlewis/react-native,ptomasroos/react-native,javache/react-native,Ehesp/react-native,myntra/react-native,skevy/react-native,Livyli/react-native,clozr/react-native,tszajna0/react-native,farazs/react-native,brentvatne/react-native,jasonnoahchoi/react-native,shrutic123/react-native,facebook/react-native,janicduplessis/react-native,clozr/react-native,hammerandchisel/react-native,peterp/react-native,Livyli/react-native,hammerandchisel/react-native,csatf/react-native,imDangerous/react-native,tszajna0/react-native,happypancake/react-native,exponent/react-native,jasonnoahchoi/react-native,thotegowda/react-native,negativetwelve/react-native,forcedotcom/react-native,ptmt/react-native-macos,skevy/react-native,PlexChat/react-native,jasonnoahchoi/react-native,kesha-antonov/react-native,adamjmcgrath/react-native,exponent/react-native,jasonnoahchoi/react-native,pandiaraj44/react-native,formatlos/react-native,chnfeeeeeef/react-native,makadaw/react-native,orenklein/react-native,tszajna0/react-native,hoastoolshop/react-native,jasonnoahchoi/react-native,rickbeerendonk/react-native,frantic/react-native,pandiaraj44/react-native,cdlewis/react-native,Maxwell2022/react-native,doochik/react-native,pandiaraj44/react-native,cdlewis/react-native,tsjing/react-native,adamjmcgrath/react-native,kesha-antonov/react-native,kesha-antonov/react-native,cpunion/react-native,tsjing/react-native,javache/react-native,hoangpham95/react-native,imDangerous/react-native,aljs/react-native,negativetwelve/react-native,imDangerous/react-native,facebook/react-native,janicduplessis/react-native,exponentjs/react-native,formatlos/react-native,tsjing/react-native,happypancake/react-native,lprhodes/react-native,doochik/react-native,gilesvangruisen/react-native,hoastoolshop/react-native,Guardiannw/react-native,negativetwelve/react-native,ptmt/react-native-macos,rickbeerendonk/react-native,aljs/react-native,janicduplessis/react-native,shrutic123/react-native,formatlos/react-native,Bhullnatik/react-native,ptmt/react-native-macos,hammerandchisel/react-native,thotegowda/react-native,ptomasroos/react-native,imDangerous/react-native,jevakallio/react-native,Swaagie/react-native,shrutic123/react-native,alin23/react-native,gilesvangruisen/react-native,javache/react-native,farazs/react-native,imDangerous/react-native,tszajna0/react-native,brentvatne/react-native,cpunion/react-native,csatf/react-native,cpunion/react-native,Maxwell2022/react-native,Ehesp/react-native,hammerandchisel/react-native,negativetwelve/react-native,ptmt/react-native-macos,Livyli/react-native,imDangerous/react-native,jevakallio/react-native,ptmt/react-native-macos,farazs/react-native,alin23/react-native,clozr/react-native,exponentjs/react-native,exponentjs/react-native,chnfeeeeeef/react-native,myntra/react-native,ptomasroos/react-native,cdlewis/react-native,adamjmcgrath/react-native,ndejesus1227/react-native,mironiasty/react-native,makadaw/react-native,Bhullnatik/react-native,peterp/react-native,ndejesus1227/react-native,kesha-antonov/react-native,hoangpham95/react-native,Maxwell2022/react-native,Livyli/react-native,cpunion/react-native,dikaiosune/react-native,ndejesus1227/react-native,imDangerous/react-native,negativetwelve/react-native,mironiasty/react-native,aljs/react-native,gilesvangruisen/react-native,facebook/react-native,hoastoolshop/react-native,hoastoolshop/react-native,negativetwelve/react-native,orenklein/react-native,rickbeerendonk/react-native,myntra/react-native,cdlewis/react-native,cpunion/react-native,lprhodes/react-native,chnfeeeeeef/react-native,tszajna0/react-native,adamjmcgrath/react-native,mironiasty/react-native,aljs/react-native,pandiaraj44/react-native,ptomasroos/react-native,exponent/react-native,skevy/react-native,doochik/react-native,Bhullnatik/react-native,brentvatne/react-native,tsjing/react-native,jevakallio/react-native,exponent/react-native,formatlos/react-native,gilesvangruisen/react-native,alin23/react-native,PlexChat/react-native,formatlos/react-native,farazs/react-native,exponent/react-native,jevakallio/react-native,makadaw/react-native,exponentjs/react-native,Swaagie/react-native,chnfeeeeeef/react-native,exponent/react-native,janicduplessis/react-native,myntra/react-native,dikaiosune/react-native,kesha-antonov/react-native,tsjing/react-native,chnfeeeeeef/react-native,formatlos/react-native,ptomasroos/react-native,dikaiosune/react-native,alin23/react-native,rickbeerendonk/react-native,chnfeeeeeef/react-native,aljs/react-native,orenklein/react-native,mironiasty/react-native,negativetwelve/react-native,csatf/react-native,brentvatne/react-native,rickbeerendonk/react-native,pandiaraj44/react-native,Maxwell2022/react-native,clozr/react-native,Bhullnatik/react-native,dikaiosune/react-native,PlexChat/react-native,negativetwelve/react-native,cpunion/react-native,jevakallio/react-native,shrutic123/react-native,peterp/react-native,rickbeerendonk/react-native,cdlewis/react-native,brentvatne/react-native,thotegowda/react-native,csatf/react-native,Bhullnatik/react-native,kesha-antonov/react-native,aljs/react-native,janicduplessis/react-native,janicduplessis/react-native,ndejesus1227/react-native,arthuralee/react-native,hoastoolshop/react-native,tsjing/react-native,javache/react-native,jevakallio/react-native,csatf/react-native,jevakallio/react-native,doochik/react-native,cpunion/react-native,ndejesus1227/react-native,frantic/react-native,orenklein/react-native,shrutic123/react-native,Ehesp/react-native,hoangpham95/react-native,rickbeerendonk/react-native,ndejesus1227/react-native,Swaagie/react-native,makadaw/react-native,Livyli/react-native,kesha-antonov/react-native,skevy/react-native,jasonnoahchoi/react-native,formatlos/react-native,gilesvangruisen/react-native,javache/react-native,csatf/react-native,tszajna0/react-native,forcedotcom/react-native,happypancake/react-native