Add note about release notes in upgrade guide
Add note about release notes in upgrade guide

It's useful to have a link to the release notes in the upgrade guide for
a clearer view of what changed in Rails.

iainbeeston/rails,mtsmfm/rails,illacceptanything/illacceptanything,rails/rails,kenta-s/rails,utilum/rails,kmayer/rails,bolek/rails,kmayer/rails,gfvcastro/rails,printercu/rails,yawboakye/rails,illacceptanything/illacceptanything,esparta/rails,riseshia/railsguides.kr,eileencodes/rails,mtsmfm/rails,brchristian/rails,elfassy/rails,Vasfed/rails,untidy-hair/rails,MichaelSp/rails,arjes/rails,xlymian/rails,Erol/rails,lcreid/rails,stefanmb/rails,richseviora/rails,Sen-Zhang/rails,gfvcastro/rails,lcreid/rails,jeremy/rails,arjes/rails,voray/rails,kmcphillips/rails,ledestin/rails,alecspopa/rails,richseviora/rails,Edouard-chin/rails,rails/rails,schuetzm/rails,Envek/rails,starknx/rails,deraru/rails,lucasmazza/rails,palkan/rails,coreyward/rails,ngpestelos/rails,notapatch/rails,elfassy/rails,EmmaB/rails-1,sergey-alekseev/rails,mijoharas/rails,tijwelch/rails,tgxworld/rails,Envek/rails,tgxworld/rails,prathamesh-sonpatki/rails,kirs/rails-1,bogdanvlviv/rails,rbhitchcock/rails,tjschuck/rails,joonyou/rails,marklocklear/rails,ngpestelos/rails,prathamesh-sonpatki/rails,hanystudy/rails,arunagw/rails,rossta/rails,rails/rails,samphilipd/rails,aditya-kapoor/rails,Vasfed/rails,illacceptanything/illacceptanything,travisofthenorth/rails,yalab/rails,mtsmfm/railstest,yawboakye/rails,pschambacher/rails,koic/rails,yhirano55/rails,bradleypriest/rails,baerjam/rails,mathieujobin/reduced-rails-for-travis,travisofthenorth/rails,EmmaB/rails-1,kamipo/rails,mechanicles/rails,brchristian/rails,Spin42/rails,lcreid/rails,flanger001/rails,brchristian/rails,sealocal/rails,eileencodes/rails,stefanmb/rails,marklocklear/rails,yalab/rails,richseviora/rails,stefanmb/rails,Erol/rails,kddeisz/rails,alecspopa/rails,illacceptanything/illacceptanything,BlakeWilliams/rails,flanger001/rails,hanystudy/rails,schuetzm/rails,mijoharas/rails,voray/rails,matrinox/rails,illacceptanything/illacceptanything,illacceptanything/illacceptanything,mathieujobin/reduced-rails-for-travis,Vasfed/rails,untidy-hair/rails,pschambacher/rails,yahonda/rails,utilum/rails,Edouard-chin/rails,jeremy/rails,yasslab/railsguides.jp,illacceptanything/illacceptanything,notapatch/rails,pvalena/rails,BlakeWilliams/rails,repinel/rails,odedniv/rails,gcourtemanche/rails,arunagw/rails,Envek/rails,gfvcastro/rails,mohitnatoo/rails,vipulnsward/rails,schuetzm/rails,utilum/rails,yalab/rails,betesh/rails,jeremy/rails,kmcphillips/rails,illacceptanything/illacceptanything,esparta/rails,hanystudy/rails,felipecvo/rails,mohitnatoo/rails,illacceptanything/illacceptanything,kirs/rails-1,betesh/rails,baerjam/rails,ledestin/rails,arunagw/rails,bolek/rails,yahonda/rails,repinel/rails,Stellenticket/rails,assain/rails,shioyama/rails,voray/rails,Spin42/rails,gcourtemanche/rails,rafaelfranca/omg-rails,sergey-alekseev/rails,riseshia/railsguides.kr,felipecvo/rails,Sen-Zhang/rails,rbhitchcock/rails,koic/rails,Stellenticket/rails,kaspth/rails,starknx/rails,ttanimichi/rails,joonyou/rails,illacceptanything/illacceptanything,lucasmazza/rails,iainbeeston/rails,deraru/rails,maicher/rails,yalab/rails,pvalena/rails,rafaelfranca/omg-rails,iainbeeston/rails,gavingmiller/rails,travisofthenorth/rails,printercu/rails,sergey-alekseev/rails,vipulnsward/rails,mohitnatoo/rails,tjschuck/rails,fabianoleittes/rails,tijwelch/rails,ngpestelos/rails,palkan/rails,odedniv/rails,gavingmiller/rails,printercu/rails,kaspth/rails,georgeclaghorn/rails,EmmaB/rails-1,joonyou/rails,xlymian/rails,gfvcastro/rails,coreyward/rails,ttanimichi/rails,utilum/rails,yahonda/rails,assain/rails,MSP-Greg/rails,baerjam/rails,odedniv/rails,kddeisz/rails,betesh/rails,bradleypriest/rails,kamipo/rails,MSP-Greg/rails,yasslab/railsguides.jp,yahonda/rails,rossta/rails,esparta/rails,mijoharas/rails,travisofthenorth/rails,deraru/rails,fabianoleittes/rails,schuetzm/rails,kachick/rails,tgxworld/rails,yawboakye/rails,arjes/rails,Stellenticket/rails,illacceptanything/illacceptanything,gavingmiller/rails,pvalena/rails,Erol/rails,yasslab/railsguides.jp,vipulnsward/rails,pvalena/rails,BlakeWilliams/rails,kaspth/rails,notapatch/rails,Spin42/rails,eileencodes/rails,MSP-Greg/rails,starknx/rails,Vasfed/rails,mohitnatoo/rails,lcreid/rails,fabianoleittes/rails,kachick/rails,kmcphillips/rails,kamipo/rails,yhirano55/rails,prathamesh-sonpatki/rails,mechanicles/rails,kddeisz/rails,tgxworld/rails,baerjam/rails,maicher/rails,ledestin/rails,bogdanvlviv/rails,Sen-Zhang/rails,Envek/rails,tijwelch/rails,mechanicles/rails,gcourtemanche/rails,sealocal/rails,xlymian/rails,prathamesh-sonpatki/rails,maicher/rails,illacceptanything/illacceptanything,joonyou/rails,iainbeeston/rails,aditya-kapoor/rails,mtsmfm/rails,matrinox/rails,gauravtiwari/rails,georgeclaghorn/rails,elfassy/rails,MichaelSp/rails,aditya-kapoor/rails,coreyward/rails,yawboakye/rails,jeremy/rails,repinel/rails,Erol/rails,kenta-s/rails,flanger001/rails,MichaelSp/rails,tjschuck/rails,felipecvo/rails,bogdanvlviv/rails,rbhitchcock/rails,rossta/rails,shioyama/rails,alecspopa/rails,illacceptanything/illacceptanything,gauravtiwari/rails,flanger001/rails,georgeclaghorn/rails,shioyama/rails,aditya-kapoor/rails,yasslab/railsguides.jp,BlakeWilliams/rails,kenta-s/rails,vipulnsward/rails,tjschuck/rails,Edouard-chin/rails,assain/rails,marklocklear/rails,gauravtiwari/rails,esparta/rails,mtsmfm/railstest,shioyama/rails,pschambacher/rails,bolek/rails,eileencodes/rails,assain/rails,MSP-Greg/rails,mathieujobin/reduced-rails-for-travis,deraru/rails,Edouard-chin/rails,lucasmazza/rails,betesh/rails,rafaelfranca/omg-rails,kachick/rails,samphilipd/rails,illacceptanything/illacceptanything,yhirano55/rails,mtsmfm/railstest,bradleypriest/rails,palkan/rails,georgeclaghorn/rails,untidy-hair/rails,arunagw/rails,palkan/rails,samphilipd/rails,riseshia/railsguides.kr,notapatch/rails,sealocal/rails,kmcphillips/rails,yhirano55/rails,kddeisz/rails,Stellenticket/rails,ttanimichi/rails,mechanicles/rails,illacceptanything/illacceptanything,untidy-hair/rails,riseshia/railsguides.kr,matrinox/rails,kirs/rails-1,koic/rails,fabianoleittes/rails,printercu/rails,rails/rails,kmayer/rails,repinel/rails,bogdanvlviv/rails