DOCSP-10334: add note on compatibility with third party APIs (#17)

* DOCSP-10334: add note on compatibility with third party APIs

Author: Chris Cho

source/kafka-compatibility.txt

@@ -16,6 +16,13 @@ Kafka Source Connector
 ----------------------
 
 The **Kafka Source Connector** requires MongoDB 3.6 or later as your data
-source if you are using change streams with a **collection** only. If you 
-need to watch a **database** or **deployment**, you need MongoDB 4.0 or 
+source if you are using change streams with a **collection** only. If you
+need to watch a **database** or **deployment**, you need MongoDB 4.0 or
 later.
+
+.. note::
+
+   MongoDB Kafka connectors are only tested against MongoDB clusters. If
+   you use the MongoDB Kafka connector with a non-genuine MongoDB database,
+   it may not function correctly due to differences in features or feature
+   behavior.