DOCSP-44692: Cluster event breaking change (#297)

(cherry picked from commit 39b7452)

Author: mcmorisi

source/upgrade/v3.txt

@@ -192,4 +192,7 @@ Version 3.0 Breaking Changes
   - Removes the ``AsDateTime`` property. Use the `AsUniversalTime <{+new-api-root+}/MongoDB.Bson/MongoDB.Bson.BsonValue.AsUniversalTime.html#MongoDB_Bson_BsonValue_AsUniversalTime>`__
     property instead. 
   - Removes the ``AsNullableDateTime`` property. Use the `AsNullableUniversalTime <{+new-api-root+}/MongoDB.Bson/MongoDB.Bson.BsonValue.AsNullableUniversalTime.html#MongoDB_Bson_BsonValue_AsNullableUniversalTime>`__
-    property instead.
+    property instead.
+
+- The driver removes individual cluster events from ``MongoClient.Cluster``. To listen for
+  cluster events, use `ClusterBuilder.Subscribe() <{+new-api-root+}/MongoDB.Driver/MongoDB.Driver.Core.Configuration.ClusterBuilder.Subscribe.html>`__.