Note about plugin files outside of their scope

Adding a note about plugins storing files or folders outside of their given scope in app/plugins/plugin-name
Merge pull request #39 from benjibee/master

Note about plugin files outside of their scope
Minor fixes to README for plugins note
Major fixes to README under Folder Structure

This is a big deal.
Merge pull request #40 from QWp6t/patch-1

Major fixes to README under Folder Structure
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Major fixes to README under Folder Structure
  Minor fixes to README for plugins note
  Note about plugin files outside of their scope