docs: create GeneralsIO client example

The with block is important, thats how the websocket connection is
automatically handled. It can be ommited by instiantiating the
GeneralsIOClient directly, but it will require manual call for
disconnect. For details, see:
https://python-socketio.readthedocs.io/en/latest/client.html#creating-a-client-instance

examples/client_example.py

@@ -0,0 +1,11 @@
+from generals.agents.random_agent import RandomAgent
+from generals.remote import GeneralsIOClient
+
+
+if __name__ == "__main__":
+    agent = RandomAgent()
+    with GeneralsIOClient(agent, "user_id9l") as client:
+        # register call will fail when given username is already registered
+        client.register_agent("[Bot]MyEpicUsername")
+        client.join_private_game("queueID")
+        client.wait_for_game()