Fix docker instructions using port 80 on localhost.
Fix docker instructions using port 80 on localhost.

This was confusing, because we otherwise suggest consistently to users
that they should connect to their development environment on port
9991.

Fixes #1032.

calvinleenyc/zulip,niftynei/zulip,tommyip/zulip,JPJPJPOPOP/zulip,rishig/zulip,grave-w-grave/zulip,SmartPeople/zulip,sharmaeklavya2/zulip,AZtheAsian/zulip,zacps/zulip,christi3k/zulip,ryanbackman/zulip,aakash-cr7/zulip,christi3k/zulip,timabbott/zulip,rishig/zulip,cosmicAsymmetry/zulip,Diptanshu8/zulip,andersk/zulip,susansls/zulip,verma-varsha/zulip,samatdav/zulip,PhilSk/zulip,punchagan/zulip,jrowan/zulip,umkay/zulip,eeshangarg/zulip,kou/zulip,krtkmj/zulip,TigorC/zulip,calvinleenyc/zulip,jrowan/zulip,cosmicAsymmetry/zulip,isht3/zulip,tommyip/zulip,dhcrzf/zulip,niftynei/zulip,arpith/zulip,Galexrt/zulip,zulip/zulip,showell/zulip,arpith/zulip,jphilipsen05/zulip,eeshangarg/zulip,PhilSk/zulip,souravbadami/zulip,TigorC/zulip,shubhamdhama/zulip,Galexrt/zulip,PhilSk/zulip,amanharitsh123/zulip,vabs22/zulip,PhilSk/zulip,hackerkid/zulip,mohsenSy/zulip,JPJPJPOPOP/zulip,timabbott/zulip,christi3k/zulip,samatdav/zulip,arpith/zulip,krtkmj/zulip,ryanbackman/zulip,mahim97/zulip,sup95/zulip,isht3/zulip,punchagan/zulip,zacps/zulip,ahmadassaf/zulip,christi3k/zulip,andersk/zulip,andersk/zulip,dawran6/zulip,jainayush975/zulip,rht/zulip,j831/zulip,cosmicAsymmetry/zulip,shubhamdhama/zulip,zulip/zulip,sup95/zulip,brainwane/zulip,dhcrzf/zulip,sonali0901/zulip,synicalsyntax/zulip,peguin40/zulip,JPJPJPOPOP/zulip,ryanbackman/zulip,vikas-parashar/zulip,sup95/zulip,joyhchen/zulip,TigorC/zulip,dhcrzf/zulip,TigorC/zulip,paxapy/zulip,TigorC/zulip,jainayush975/zulip,Galexrt/zulip,andersk/zulip,jrowan/zulip,rht/zulip,calvinleenyc/zulip,mahim97/zulip,cosmicAsymmetry/zulip,AZtheAsian/zulip,dawran6/zulip,showell/zulip,tommyip/zulip,grave-w-grave/zulip,joyhchen/zulip,ahmadassaf/zulip,Galexrt/zulip,jrowan/zulip,Diptanshu8/zulip,vikas-parashar/zulip,zacps/zulip,PhilSk/zulip,vikas-parashar/zulip,ahmadassaf/zulip,souravbadami/zulip,synicalsyntax/zulip,jackrzhang/zulip,jackrzhang/zulip,rht/zulip,timabbott/zulip,synicalsyntax/zulip,jrowan/zulip,dattatreya303/zulip,jphilipsen05/zulip,mohsenSy/zulip,andersk/zulip,arpith/zulip,shubhamdhama/zulip,jainayush975/zulip,ahmadassaf/zulip,punchagan/zulip,samatdav/zulip,AZtheAsian/zulip,Jianchun1/zulip,souravbadami/zulip,niftynei/zulip,JPJPJPOPOP/zulip,Juanvulcano/zulip,christi3k/zulip,mahim97/zulip,Juanvulcano/zulip,SmartPeople/zulip,KingxBanana/zulip,krtkmj/zulip,dattatreya303/zulip,AZtheAsian/zulip,umkay/zulip,sharmaeklavya2/zulip,mahim97/zulip,eeshangarg/zulip,blaze225/zulip,blaze225/zulip,jphilipsen05/zulip,Diptanshu8/zulip,AZtheAsian/zulip,jphilipsen05/zulip,peguin40/zulip,brainwane/zulip,vaidap/zulip,JPJPJPOPOP/zulip,brainwane/zulip,jackrzhang/zulip,dhcrzf/zulip,amanharitsh123/zulip,zulip/zulip,sup95/zulip,rht/zulip,susansls/zulip,amanharitsh123/zulip,showell/zulip,timabbott/zulip,dawran6/zulip,sonali0901/zulip,Diptanshu8/zulip,ahmadassaf/zulip,jackrzhang/zulip,zacps/zulip,showell/zulip,souravbadami/zulip,krtkmj/zulip,brockwhittaker/zulip,jackrzhang/zulip,paxapy/zulip,rishig/zulip,sharmaeklavya2/zulip,ryanbackman/zulip,Jianchun1/zulip,Juanvulcano/zulip,Diptanshu8/zulip,aakash-cr7/zulip,Jianchun1/zulip,brockwhittaker/zulip,brainwane/zulip,verma-varsha/zulip,KingxBanana/zulip,tommyip/zulip,shubhamdhama/zulip,dattatreya303/zulip,vabs22/zulip,amyliu345/zulip,aakash-cr7/zulip,sup95/zulip,mohsenSy/zulip,hackerkid/zulip,paxapy/zulip,joyhchen/zulip,synicalsyntax/zulip,samatdav/zulip,tommyip/zulip,eeshangarg/zulip,jackrzhang/zulip,j831/zulip,brainwane/zulip,shubhamdhama/zulip,TigorC/zulip,vabs22/zulip,verma-varsha/zulip,AZtheAsian/zulip,verma-varsha/zulip,isht3/zulip,krtkmj/zulip,zulip/zulip,peguin40/zulip,dawran6/zulip,brainwane/zulip,reyha/zulip,calvinleenyc/zulip,reyha/zulip,cosmicAsymmetry/zulip,samatdav/zulip,amyliu345/zulip,kou/zulip,kou/zulip,j831/zulip,KingxBanana/zulip,kou/zulip,susansls/zulip,umkay/zulip,showell/zulip,j831/zulip,ahmadassaf/zulip,joyhchen/zulip,niftynei/zulip,kou/zulip,sharmaeklavya2/zulip,sharmaeklavya2/zulip,zacps/zulip,dattatreya303/zulip,j831/zulip,paxapy/zulip,isht3/zulip,SmartPeople/zulip,jackrzhang/zulip,vaidap/zulip,Juanvulcano/zulip,KingxBanana/zulip,brockwhittaker/zulip,Diptanshu8/zulip,umkay/zulip,jainayush975/zulip,vikas-parashar/zulip,sup95/zulip,umkay/zulip,reyha/zulip,ahmadassaf/zulip,paxapy/zulip,blaze225/zulip,vaidap/zulip,shubhamdhama/zulip,rishig/zulip,blaze225/zulip,SmartPeople/zulip,souravbadami/zulip,ryanbackman/zulip,punchagan/zulip,verma-varsha/zulip,amyliu345/zulip,brockwhittaker/zulip,reyha/zulip,hackerkid/zulip,vabs22/zulip,paxapy/zulip,dattatreya303/zulip,grave-w-grave/zulip,KingxBanana/zulip,joyhchen/zulip,isht3/zulip,timabbott/zulip,vikas-parashar/zulip,peguin40/zulip,punchagan/zulip,zacps/zulip,umkay/zulip,kou/zulip,Jianchun1/zulip,synicalsyntax/zulip,dhcrzf/zulip,showell/zulip,Juanvulcano/zulip,vaidap/zulip,Galexrt/zulip,Jianchun1/zulip,timabbott/zulip,sonali0901/zulip,reyha/zulip,blaze225/zulip,rishig/zulip,verma-varsha/zulip,zulip/zulip,SmartPeople/zulip,grave-w-grave/zulip,amyliu345/zulip,isht3/zulip,hackerkid/zulip,christi3k/zulip,jphilipsen05/zulip,brockwhittaker/zulip,PhilSk/zulip,amyliu345/zulip,j831/zulip,arpith/zulip,aakash-cr7/zulip,krtkmj/zulip,calvinleenyc/zulip,Juanvulcano/zulip,niftynei/zulip,SmartPeople/zulip,reyha/zulip,calvinleenyc/zulip,brainwane/zulip,synicalsyntax/zulip,niftynei/zulip,showell/zulip,amanharitsh123/zulip,synicalsyntax/zulip,susansls/zulip,mahim97/zulip,grave-w-grave/zulip,jainayush975/zulip,rishig/zulip,dawran6/zulip,sonali0901/zulip,vabs22/zulip,Jianchun1/zulip,grave-w-grave/zulip,amanharitsh123/zulip,zulip/zulip,shubhamdhama/zulip,mohsenSy/zulip,aakash-cr7/zulip,dhcrzf/zulip,rht/zulip,blaze225/zulip,tommyip/zulip,kou/zulip,zulip/zulip,vikas-parashar/zulip,susansls/zulip,umkay/zulip,joyhchen/zulip,Galexrt/zulip,rht/zulip,timabbott/zulip,tommyip/zulip,eeshangarg/zulip,vaidap/zulip,amyliu345/zulip,sonali0901/zulip,dhcrzf/zulip,punchagan/zulip,KingxBanana/zulip,mohsenSy/zulip,hackerkid/zulip,dattatreya303/zulip,jainayush975/zulip,hackerkid/zulip,hackerkid/zulip,peguin40/zulip,arpith/zulip,mahim97/zulip,mohsenSy/zulip,amanharitsh123/zulip,Galexrt/zulip,JPJPJPOPOP/zulip,brockwhittaker/zulip,sharmaeklavya2/zulip,punchagan/zulip,samatdav/zulip,andersk/zulip,souravbadami/zulip,vaidap/zulip,krtkmj/zulip,rishig/zulip,andersk/zulip,peguin40/zulip,cosmicAsymmetry/zulip,aakash-cr7/zulip,dawran6/zulip,rht/zulip,jrowan/zulip,susansls/zulip,jphilipsen05/zulip,ryanbackman/zulip,sonali0901/zulip,eeshangarg/zulip,vabs22/zulip,eeshangarg/zulip