[DOC] mail_mailgun: doc/index.rst formattings and new paragraph

mail_mailgun/doc/index.rst

@@ -28,6 +28,13 @@ Usage
 * Edit Messaging Alias for your user. Now you can receive emails that is sent to configured alias email address.
 
   * From menu Settings/Users/Users open you user and click 'Edit'
- * On Preference tab put alias into Messaging Alias field and click 'Save'
+  * On Preference tab put alias into Messaging Alias field and click 'Save'. E.g. ``admin@sandbox...mailgun.org``
+
+* Send email on ``admin@sandox...mailgun.org``
+* Open ``Discuss`` from odoo
+* See your message there
+* Stop odoo and send several emails again. On odoo starting you see all your messages in ``Discuss``
+
+