Docs, queryset.update: full_result-arg not clearly described

The documentation for the `full_result`-argument to `queryset.update()`
can be read as returning the update documents/objects, whereas it's
really returning just the full "PyMongo result dictionary".

This commit adds some wording and an example dictionary,
to make it clear what the behavior is.

Author: malthejorgensen

mongoengine/queryset/base.py

@@ -486,8 +486,9 @@ def update(self, upsert=False, multi=True, write_concern=None,
             ``save(..., write_concern={w: 2, fsync: True}, ...)`` will
             wait until at least two servers have recorded the write and
             will force an fsync on the primary server.
-        :param full_result: Return the full result rather than just the number
-            updated.
+        :param full_result: Return the full result dictionary rather than just the number
+            updated, e.g. return
+            `{u'n': 2, u'nModified': 2, u'ok': 1.0, 'updatedExisting': True}`.
         :param update: Django-style update keyword arguments
 
         .. versionadded:: 0.2