Update events.rst

Part translation in french
Added a How to Install Plugins guide
Merge pull request #1951 from cakephp/2.x-how-to-install-plugins

Added a How to Install Plugins guide
Merge pull request #1539 from ExtraBlind/patch-1

Update events.rst
update after #1539
Updated getCrumbs signature

Closes https://github.com/cakephp/docs/pull/1955