[LYN-4366] Add API documentation for AzNetworking, Mutiplayer Gem, and Multiplayer Compression Gem classes.

Signed-off-by: stramer <stramer@amazon.com>

Code/Framework/AzNetworking/AzNetworking/Serialization/ISerializer.h

@@ -27,6 +27,18 @@ namespace AzNetworking
 
     //! @class ISerializer
     //! @brief Interface class for all serializers to derive from.
+    //!
+    //! ISerializer defines an abstract interface for visiting an object hierarchy and performing operations upon that hierarchy,
+    //! typically reading from or writing data to the object hierarchy for reasons of persistence or network transmission.
+    //! 
+    //! While the most common types of serializers are provided by the AzNetworking framework, users can implement custom
+    //! serializers and perform complex operations on any serializable structures. A few types native to AzNetworking, many of which
+    //! relate to packets, demonstrate this.
+    //! 
+    //! Provided serializers include NetworkInputSerializer for writing an object model into a bytestream, NetworkOutputSerializer
+    //! for writing to an object model, TrackChangesSerializer which is used to efficiently serialize objects without incurring significant
+    //! copy or comparison overhead, and HashSerializer which can be used to generate a hash of all visited data which is important for
+    //! automated desync detection. 
     class ISerializer
     {
     public: