Add example E2e client

e2eClient/README.md

+# xxdk E2E client example
+
+This mini-repository contains example logic for running an e2e client.  
+This is provided by the xx network team as a springboard to help consumers 
+better understand our API and how it may be used.
+
+`main.go` contains the crux of the logic. We avoid complicating our example by
+avoiding the usage of CLI flags for basic variables you may change in the code.
+This file initiates an xxdk E2E client, using the authentication callbacks in
+`auth.go`. With that established, it registers a generic message listener 
+and establishes authentication with a partner.  Finally, it sends a test message 
+and listens for incoming messages until stopped by the user.
+
+`utils.go` contains utility functions for running the program. In this case,
+we provide a tool initializing a log and one which writes a contact to a file.
+
+`listener.go` contains logic for handling the reception of a message via the
+e2e client. In this example, it is very basic. We invite consumers
+to use this as a basis to implement more complex message listeners.
+
+## Build Instructions
+
+In these instructions we will go over building a connection client using our
+example. In order to build a client which successfully sends a message through
+the connection, we must first go over how to build and run a connection server.
+
+### Building a Client