Add a geo example using $maxDistance.

Author: behackett

doc/examples/geo.rst

@@ -59,6 +59,18 @@ Using the geospatial index we can find documents near another point:
  "{u'loc': [4, 4], u'_id': ObjectId('...')}"
  "{u'loc': [1, 2], u'_id': ObjectId('...')}"
 
+The $maxDistance operator requires the use of :class:`~bson.son.SON`:
+
+.. doctest::
+
+ >>> from bson.son import SON
+ >>> for doc in db.places.find({"loc": SON([("$near", [3, 6]), ("$maxDistance", 100)])}).limit(3):
+ ... repr(doc)
+ ...
+ "{u'loc': [2, 5], u'_id': ObjectId('...')}"
+ "{u'loc': [4, 4], u'_id': ObjectId('...')}"
+ "{u'loc': [1, 2], u'_id': ObjectId('...')}"
+
 It's also possible to query for all items within a given rectangle
 (specified by lower-left and upper-right coordinates):