Fix code indentation and improve formatting
Fix code indentation and improve formatting

in the Getting Started Guide.

This PR regroups #14817, #14818 and #14819 into one commit.

[skip ci]
kirs/rails-1,utilum/rails,yhirano55/rails,kenta-s/rails,Envek/rails,rossta/rails,mtsmfm/railstest,tjschuck/rails,fabianoleittes/rails,Sen-Zhang/rails,notapatch/rails,bolek/rails,coreyward/rails,lcreid/rails,palkan/rails,amoody2108/TechForJustice,Vasfed/rails,marklocklear/rails,brchristian/rails,odedniv/rails,samphilipd/rails,georgeclaghorn/rails,pvalena/rails,georgeclaghorn/rails,kddeisz/rails,mathieujobin/reduced-rails-for-travis,gfvcastro/rails,voray/rails,illacceptanything/illacceptanything,joonyou/rails,esparta/rails,Spin42/rails,ledestin/rails,yalab/rails,rails/rails,ngpestelos/rails,prathamesh-sonpatki/rails,voray/rails,mechanicles/rails,shioyama/rails,utilum/rails,vipulnsward/rails,untidy-hair/rails,jeremy/rails,fabianoleittes/rails,deraru/rails,mohitnatoo/rails,printercu/rails,BlakeWilliams/rails,georgeclaghorn/rails,yahonda/rails,vassilevsky/rails,gavingmiller/rails,untidy-hair/rails,yawboakye/rails,hanystudy/rails,rafaelfranca/omg-rails,maicher/rails,Vasfed/rails,odedniv/rails,yawboakye/rails,Erol/rails,palkan/rails,yhirano55/rails,yasslab/railsguides.jp,mtsmfm/rails,stefanmb/rails,eileencodes/rails,sealocal/rails,koic/rails,rbhitchcock/rails,sergey-alekseev/rails,alecspopa/rails,utilum/rails,kamipo/rails,kenta-s/rails,88rabbit/newRails,lucasmazza/rails,kaspth/rails,MichaelSp/rails,yalab/rails,pvalena/rails,felipecvo/rails,bradleypriest/rails,alecspopa/rails,kmcphillips/rails,gfvcastro/rails,yalab/rails,rails/rails,Stellenticket/rails,gfvcastro/rails,MichaelSp/rails,joonyou/rails,elfassy/rails,stefanmb/rails,maicher/rails,betesh/rails,gauravtiwari/rails,odedniv/rails,rails/rails,prathamesh-sonpatki/rails,ledestin/rails,alecspopa/rails,mijoharas/rails,yahonda/rails,mtsmfm/rails,yawboakye/rails,notapatch/rails,Edouard-chin/rails,vassilevsky/rails,gcourtemanche/rails,tgxworld/rails,coreyward/rails,Erol/rails,Spin42/rails,deraru/rails,riseshia/railsguides.kr,mechanicles/rails,tijwelch/rails,lcreid/rails,tjschuck/rails,tgxworld/rails,Sen-Zhang/rails,Stellenticket/rails,Stellenticket/rails,rossta/rails,bolek/rails,notapatch/rails,illacceptanything/illacceptanything,kamipo/rails,illacceptanything/illacceptanything,kaspth/rails,voray/rails,arjes/rails,illacceptanything/illacceptanything,gfvcastro/rails,eileencodes/rails,Edouard-chin/rails,shioyama/rails,kaspth/rails,shioyama/rails,yhirano55/rails,sergey-alekseev/rails,yalab/rails,elfassy/rails,hanystudy/rails,amoody2108/TechForJustice,MSP-Greg/rails,elfassy/rails,mtsmfm/rails,shioyama/rails,gavingmiller/rails,Vasfed/rails,richseviora/rails,koic/rails,baerjam/rails,yhirano55/rails,illacceptanything/illacceptanything,eileencodes/rails,prathamesh-sonpatki/rails,assain/rails,yahonda/rails,eileencodes/rails,illacceptanything/illacceptanything,amoody2108/TechForJustice,betesh/rails,EmmaB/rails-1,kamipo/rails,lucasmazza/rails,repinel/rails,untidy-hair/rails,mohitnatoo/rails,illacceptanything/illacceptanything,Spin42/rails,mtsmfm/railstest,travisofthenorth/rails,kirs/rails-1,illacceptanything/illacceptanything,pschambacher/rails,vipulnsward/rails,tgxworld/rails,tjschuck/rails,mathieujobin/reduced-rails-for-travis,baerjam/rails,bolek/rails,marklocklear/rails,vipulnsward/rails,illacceptanything/illacceptanything,MSP-Greg/rails,mijoharas/rails,assain/rails,flanger001/rails,yasslab/railsguides.jp,yasslab/railsguides.jp,hanystudy/rails,georgeclaghorn/rails,travisofthenorth/rails,Envek/rails,flanger001/rails,lcreid/rails,ttanimichi/rails,gcourtemanche/rails,Sen-Zhang/rails,xlymian/rails,illacceptanything/illacceptanything,betesh/rails,arunagw/rails,bradleypriest/rails,kmayer/rails,matrinox/rails,bradleypriest/rails,tjschuck/rails,rbhitchcock/rails,rafaelfranca/omg-rails,yawboakye/rails,pvalena/rails,palkan/rails,pvalena/rails,arunagw/rails,Edouard-chin/rails,BlakeWilliams/rails,tgxworld/rails,bogdanvlviv/rails,schuetzm/rails,iainbeeston/rails,esparta/rails,kirs/rails-1,rails/rails,felipecvo/rails,deraru/rails,illacceptanything/illacceptanything,palkan/rails,BlakeWilliams/rails,joonyou/rails,flanger001/rails,bogdanvlviv/rails,jeremy/rails,flanger001/rails,sergey-alekseev/rails,rafaelfranca/omg-rails,travisofthenorth/rails,schuetzm/rails,ttanimichi/rails,ngpestelos/rails,deraru/rails,baerjam/rails,kmcphillips/rails,koic/rails,EmmaB/rails-1,matrinox/rails,notapatch/rails,kachick/rails,illacceptanything/illacceptanything,fabianoleittes/rails,schuetzm/rails,starknx/rails,Envek/rails,Stellenticket/rails,lucasmazza/rails,Erol/rails,bogdanvlviv/rails,mechanicles/rails,jeremy/rails,Erol/rails,88rabbit/newRails,repinel/rails,illacceptanything/illacceptanything,xlymian/rails,esparta/rails,coreyward/rails,tijwelch/rails,gauravtiwari/rails,iainbeeston/rails,mijoharas/rails,assain/rails,ngpestelos/rails,kachick/rails,Vasfed/rails,rossta/rails,esparta/rails,starknx/rails,mathieujobin/reduced-rails-for-travis,samphilipd/rails,illacceptanything/illacceptanything,printercu/rails,bogdanvlviv/rails,Edouard-chin/rails,repinel/rails,mtsmfm/railstest,88rabbit/newRails,aditya-kapoor/rails,kma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