Add note to Railtie docs to use unique filenames
Add note to Railtie docs to use unique filenames

The fact that the names need to be globally unique was not obvious to me, so I
thought it'd be worth documenting. This not being clear was the cause of both
ctran/annotate_models#468 and instructure/outrigger#1.

[ci skip]

gauravtiwari/rails,illacceptanything/illacceptanything,utilum/rails,untidy-hair/rails,pvalena/rails,kamipo/rails,vipulnsward/rails,maicher/rails,assain/rails,illacceptanything/illacceptanything,kmayer/rails,mohitnatoo/rails,yasslab/railsguides.jp,Sen-Zhang/rails,Stellenticket/rails,tgxworld/rails,prathamesh-sonpatki/rails,brchristian/rails,kamipo/rails,kirs/rails-1,yawboakye/rails,printercu/rails,maicher/rails,illacceptanything/illacceptanything,repinel/rails,baerjam/rails,travisofthenorth/rails,deraru/rails,shioyama/rails,mohitnatoo/rails,arunagw/rails,iainbeeston/rails,odedniv/rails,betesh/rails,lcreid/rails,starknx/rails,MSP-Greg/rails,assain/rails,eileencodes/rails,betesh/rails,kmcphillips/rails,printercu/rails,schuetzm/rails,untidy-hair/rails,kirs/rails-1,Sen-Zhang/rails,kmcphillips/rails,kmayer/rails,illacceptanything/illacceptanything,Erol/rails,EmmaB/rails-1,rafaelfranca/omg-rails,MSP-Greg/rails,illacceptanything/illacceptanything,joonyou/rails,fabianoleittes/rails,lcreid/rails,eileencodes/rails,kddeisz/rails,iainbeeston/rails,brchristian/rails,utilum/rails,tjschuck/rails,ttanimichi/rails,Vasfed/rails,felipecvo/rails,MSP-Greg/rails,repinel/rails,illacceptanything/illacceptanything,illacceptanything/illacceptanything,deraru/rails,EmmaB/rails-1,printercu/rails,bogdanvlviv/rails,kaspth/rails,arunagw/rails,shioyama/rails,bogdanvlviv/rails,utilum/rails,betesh/rails,felipecvo/rails,schuetzm/rails,notapatch/rails,rails/rails,kddeisz/rails,iainbeeston/rails,yhirano55/rails,Erol/rails,odedniv/rails,illacceptanything/illacceptanything,Edouard-chin/rails,assain/rails,vipulnsward/rails,gauravtiwari/rails,maicher/rails,aditya-kapoor/rails,Stellenticket/rails,assain/rails,iainbeeston/rails,esparta/rails,prathamesh-sonpatki/rails,yawboakye/rails,mohitnatoo/rails,BlakeWilliams/rails,Vasfed/rails,shioyama/rails,yahonda/rails,deraru/rails,rails/rails,gauravtiwari/rails,yasslab/railsguides.jp,tgxworld/rails,joonyou/rails,yasslab/railsguides.jp,travisofthenorth/rails,kirs/rails-1,notapatch/rails,odedniv/rails,illacceptanything/illacceptanything,brchristian/rails,baerjam/rails,schuetzm/rails,baerjam/rails,Envek/rails,untidy-hair/rails,rafaelfranca/omg-rails,ledestin/rails,MSP-Greg/rails,mechanicles/rails,kamipo/rails,yhirano55/rails,tgxworld/rails,jeremy/rails,jeremy/rails,arunagw/rails,ledestin/rails,felipecvo/rails,georgeclaghorn/rails,ledestin/rails,Stellenticket/rails,Erol/rails,alecspopa/rails,betesh/rails,palkan/rails,baerjam/rails,travisofthenorth/rails,tjschuck/rails,alecspopa/rails,kddeisz/rails,mechanicles/rails,hanystudy/rails,alecspopa/rails,ttanimichi/rails,EmmaB/rails-1,Edouard-chin/rails,Edouard-chin/rails,illacceptanything/illacceptanything,yahonda/rails,rails/rails,hanystudy/rails,vipulnsward/rails,kaspth/rails,Envek/rails,pvalena/rails,yalab/rails,rails/rails,Vasfed/rails,mathieujobin/reduced-rails-for-travis,fabianoleittes/rails,Edouard-chin/rails,tjschuck/rails,yhirano55/rails,starknx/rails,tgxworld/rails,BlakeWilliams/rails,prathamesh-sonpatki/rails,bogdanvlviv/rails,starknx/rails,flanger001/rails,gcourtemanche/rails,gfvcastro/rails,travisofthenorth/rails,gcourtemanche/rails,yawboakye/rails,eileencodes/rails,fabianoleittes/rails,gfvcastro/rails,notapatch/rails,palkan/rails,printercu/rails,utilum/rails,aditya-kapoor/rails,aditya-kapoor/rails,yalab/rails,fabianoleittes/rails,mechanicles/rails,palkan/rails,aditya-kapoor/rails,yahonda/rails,joonyou/rails,georgeclaghorn/rails,illacceptanything/illacceptanything,schuetzm/rails,Sen-Zhang/rails,ttanimichi/rails,BlakeWilliams/rails,arunagw/rails,shioyama/rails,illacceptanything/illacceptanything,deraru/rails,Envek/rails,eileencodes/rails,flanger001/rails,Stellenticket/rails,flanger001/rails,Erol/rails,kmcphillips/rails,pvalena/rails,yhirano55/rails,illacceptanything/illacceptanything,repinel/rails,illacceptanything/illacceptanything,yasslab/railsguides.jp,gfvcastro/rails,mohitnatoo/rails,Vasfed/rails,lcreid/rails,yalab/rails,jeremy/rails,georgeclaghorn/rails,esparta/rails,joonyou/rails,notapatch/rails,kmayer/rails,gfvcastro/rails,pvalena/rails,kmcphillips/rails,untidy-hair/rails,mathieujobin/reduced-rails-for-travis,illacceptanything/illacceptanything,mathieujobin/reduced-rails-for-travis,palkan/rails,jeremy/rails,yahonda/rails,esparta/rails,flanger001/rails,yawboakye/rails,BlakeWilliams/rails,vipulnsward/rails,gcourtemanche/rails,hanystudy/rails,repinel/rails,georgeclaghorn/rails,bogdanvlviv/rails,rafaelfranca/omg-rails,esparta/rails,mechanicles/rails,matrinox/rails,kddeisz/rails,Envek/rails,yalab/rails,matrinox/rails,kaspth/rails,prathamesh-sonpatki/rails,matrinox/rails,tjschuck/rails,lcreid/rails