Update README.md

Author: benjchristensen

README.md

@@ -2,7 +2,7 @@
 
 ReactiveSocket is (being developed to be a) network protocol with client and server implementations following <a href="http://reactive-streams.org">Reactive Streams</a> semantics.
 
-It enables the following interaction models via async message passing over a single network connection:
+It enables the following symmetric interaction models via async message passing over a single network connection:
 
 - request/response (stream of 1)
 - request/stream (finite stream of many)
@@ -11,6 +11,7 @@ It enables the following interaction models via async message passing over a sin
 
 Artifacts include:
 
+- [Motivation.md](https://github.com/ReactiveSocket/reactivesocket/blob/master/Motivation.md): Motivation for creating this protocol.
 - [DesignPrinciples.md](https://github.com/ReactiveSocket/reactivesocket/blob/master/DesignPrinciples.md): Design and Architectural principles and context for the protocol and how it will be used.
 - [Protocol.md](https://github.com/ReactiveSocket/reactivesocket/blob/master/Protocol.md): The protocol definition.