Merge pull request #11201 from jetthoughts/fix_create_post_example_in_getting_started

Improve Getting Started Guide
remove string based terminators for `ActiveSupport::Callbacks`.
fix typo in Active Support CHANGELOG. [ci skip]
explain how to extend application templates. [ci skip]
Revert "remove string based terminators for `ActiveSupport::Callbacks`."

This reverts commit d108672dada7ba97d3b3b56f0c6001cea621061e.

Conflicts:

	activesupport/CHANGELOG.md
 #11288: Removed duplicated touching

if belongs to model with touch option on touch

Closes #11288