updating user guide: should use official civicrm repository and include a 4.7 branch

app/config/books/user.yml

 name: User guide
+description: Aimed at day to day users of CiviCRM.
 langs:
     en:
         repo: 'https://github.com/civicrm/civicrm-user-guide'
         latest: master
         stable: 4.7
         history:
-            - 4.7
             - 4.6