First draft of the bundle installation instructions
Applied all the fixes and suggestions made by reviewers
Fixed minor typo
More improvements based on reviewers' comments
Fixed some code formatting
Removed the first person perspective and other minor fixes
More tweaks and fixes
Minor fixes and tweaks
Removed the sidebar and made some minor tweaks
Reworded a bit the installation instructions
Added the fixes suggested by Ryan
feature #4236 Javiereguiluz bundle install instructions (WouterJ)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #4236).

Discussion
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Javiereguiluz bundle install instructions

Replaces https://github.com/symfony/symfony-docs/pull/4163

Commits
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7097070 Added the fixes suggested by Ryan
35dddba Reworded a bit the installation instructions
7a6644b Removed the sidebar and made some minor tweaks
41ce2a5 Minor fixes and tweaks
4b29de2 More tweaks and fixes
322ec60 Removed the first person perspective and other minor fixes
c39f7d3 Fixed some code formatting
ed96447 More improvements based on reviewers' comments
21ce2c0 Fixed minor typo
11db860 Applied all the fixes and suggestions made by reviewers
b297d29 First draft of the bundle installation instructions