Feature/improve docs

[rochamarcelo]

• Added quick sections in the home

  • I want to extend
  • I want to enable|disable
  • I want to allow access to
  • I want to customize my login page to
  • I want to add custom logic before
  • I want to add custom logic after

• Added page Docs/Documentation/Permissions.md that shows how to add permissions rules

• Improved page Docs/Documentation/Events.md with code sample with multiple events available.

• Mentioning config/users.php instead of using Configure::write

[steinkel]

:clap: :clap: :clap: