[ci skip] Add missing blank line to AR validation.
[ci skip] No need to indent here (AC overview).
[ci skip] Add highlight to code (form helper guide).
development.rb should mention available log levels
Revert "development.rb should mention available log levels"

This reverts commit 102ba5fd69f18c7d58d70247090fbdeadfc53ca1.

Reason: code/template changes cannot be made in docrails
Merge branch 'master' of github.com:rails/rails