Docu: add initial protocol docu

doc/protocol.md

@@ -0,0 +1,49 @@
+InstantChat WebSocket Protocol
+==============================
+
+Messages from client to server (commands)
+-----------------------------------------
+
+JSON objects. Key `action` determines type of message.
+
+### init
+Initialize the connection, set nickname and join/create a chat.
+
+**Parameters:**
+* `action` = `"init"`
+* `chat_id`: either an existing ID of a chat instance or *[TODO: ?]* empty string to
+  create a new chat
+* `nickname`: user's chosen nickname *[TODO: valid characters?]*
+
+**Example:**
+
+    {
+        "action": "init",
+        "chat_id": "42",
+        "nickname": "Alice"
+    }
+
+### send (?)
+Send a message...
+
+*[TODO]*
+
+
+Messages from server to client (responses/events)
+-------------------------------------------------
+
+JSON objects. Key `type` determines type of message.
+
+### init
+Response to `init` command. Confirms initialization and chat join.
+
+**Parameters:**
+* `type` = `"init"`
+* ***[TODO]***
+
+**Example:**
+
+    {
+        "type": "init",
+        TODO ???
+    }