docs: update README

Author: darrachequesne

Diff for: README.md

@@ -3,7 +3,14 @@
 
 An alternative to the default [socket.io-parser](https://github.com/socketio/socket.io-parser), encoding and decoding packets with [msgpack](http://msgpack.org/).
 
-With that parser, the browser build will be a bit heavier (an additional 7.5 KB minified, 3.0 KB gzipped), but each message will be smaller (sent as binary).
+With that parser, the browser build will be a bit heavier (an additional 7.5 KB minified, 3.0 KB gzipped), but each message will be smaller (sent as binary).
+
+Please note that you MUST use the parser on both sides (server & client).
+
+See also:
+
+- the default parser: https://github.com/socketio/socket.io-parser
+- a parser based on JSON.stringify/parse: https://github.com/darrachequesne/socket.io-json-parser
 
 ## Usage
 
@@ -12,15 +19,33 @@ const io = require('socket.io');
 const ioc = require('socket.io-client');
 const customParser = require('socket.io-msgpack-parser');
 
-let server = io(PORT, {
+const server = io(PORT, {
   parser: customParser
 });
 
-let client = ioc('ws://localhost:' + PORT, {
+const socket = ioc('ws://localhost:' + PORT, {
   parser: customParser
 });
 
-client.on('connect', () => {
-  client.emit('hello');
+socket.on('connect', () => {
+  socket.emit('hello');
 });
 ```
+
+## Format
+
+`socket.emit('hello', 'you')` will create the following packet:
+
+```json
+{
+  "type": 2,
+  "nsp": "/",
+  "data": ["hello", "you"]
+}
+```
+
+which will be encoded by the parser as:
+
+`<Buffer 83 a4 74 79 70 65 02 a3 6e 73 70 a1 2f a4 64 61 74 61 92 a5 68 65 6c 6c 6f a3 79 6f 75>`
+
+More information about the exchange protocol can be found [here](https://github.com/socketio/socket.io-protocol).