Add link to M220N courseware (#660)

add link to M220N course

Author: MongoCaleb

source/csharp.txt

@@ -28,6 +28,30 @@ with MongoDB.
 
 - `Source Code <https://github.com/mongodb/mongo-csharp-driver>`_
 
+Take the free online course taught by MongoDB
+---------------------------------------------
+
+.. list-table::
+
+   * - .. cssclass:: bordered-figure
+       .. figure:: /figures/M220N.png
+          lightbox: false
+          width: 300px
+
+     - `M220N: MongoDB for .NET Developers <https://university.mongodb.com/courses/M220N/about>`__
+        Learn the essentials of C# & ASP.NET application development with MongoDB.
+
+.. figure:: /path or uri.png
+   :alt: Alt text for the image
+   :figwidth:
+   :width:
+   :scale:
+   :align:
+   :lightbox:
+   :class:
+   
+    Optional caption for the figure.
+
 
 Installation
 ------------