Add Plugin Deactivation & Deletion section

* Add Plugin Deactivation & Deletion section to readme
Verbiage changes
Squashed 'includes/libraries/aihrus-framework/' changes from 34e9a21..9a3214e

9a3214e Coding standard

git-subtree-dir: includes/libraries/aihrus-framework
git-subtree-split: 9a3214e90f44acc8da8411090b3c0c70b089972b
Merge commit 'a75e44ac38616b85b535e1ef2c63c8212fe2e5d0' into 3.0.0RC1