DOCSP-46293 Add GUID to BSON mapping bullet (#408)

Author: jordan-smith721

source/upgrade/v3.txt

@@ -116,7 +116,10 @@ Version 3.0 Breaking Changes
   - The ``BsonBinaryData.GuidRepresentation`` property has been removed. 
   - You can call the ``BsonBinaryData.ToGuid()`` method only on ``BsonBinaryData``
     objects of subtype 4. If the object has any other subtype, you must call the
-    ``BsonBinaryData.ToGuid(GuidRepresentation)`` method and specify the subtype. 
+    ``BsonBinaryData.ToGuid(GuidRepresentation)`` method and specify the subtype.
+  - GUID conversion by using the ``BsonTypeMapper`` class has been removed. To
+    convert ``GUID`` values to BSON, use the ``BsonBindaryData(<GUID>,
+    GuidRepresentation.Standard)`` constructor.
 
   The preceding changes affect your application only if you serialize and deserialize
   BSON documents directly. If you map your MongoDB documents only to :ref:`csharp-poco`,