Update signalling server readme

Author: mickel8

signalling_server/README.md

@@ -1,21 +1,26 @@
 # SignallingServer
 
-**TODO: Add description**
+Simple signalling server for connecting two ICE peers.
 
-## Installation
+It creates a single room where only two peers can join. 
+Every message sent by one peer will be forwarded to the other peer.
 
-If [available in Hex](https://hex.pm/docs/publish), the package can be installed
-by adding `signalling_server` to your list of dependencies in `mix.exs`:
 
-```elixir
-def deps do
-  [
-    {:signalling_server, "~> 0.1.0"}
-  ]
-end
+1. Connect as 
+
+```js
+sock  = new WebSocket("ws://localhost:4000/websocket")
+```
+
+2. When the other peer connects, the signalling server sends simple info JSON:
+
+```json
+{
+  "type": "peer_joined", 
+  "role": "controlled"
+}
 ```
 
-Documentation can be generated with [ExDoc](https://github.com/elixir-lang/ex_doc)
-and published on [HexDocs](https://hexdocs.pm). Once published, the docs can
-be found at <https://hexdocs.pm/signalling_server>.
+The `role` field is a role a peer that received info JSON should use to avoid role conflict.
 
+3. Send any message via WS, it will be forwarded to the other side.