Add benchmark to Websockets

_docs/websockets.md

@@ -37,3 +37,44 @@ ws "/" do |socket|
   end
 end
 ```
+
+## Performance
+
+Thanks to Crystal Kemal has superb performance for Websockets.
+
+Crystal 0.9.1 with [Kemal]
+
+```ruby
+require "kemal"
+
+ws "/" do |socket|
+  socket.on_message do |message|
+  end
+end
+```
+
+Node.js v4.2.1 with [ws](https://github.com/websockets/ws)
+
+```js
+var WebSocketServer = require('ws').Server
+  , wss = new WebSocketServer({ port: 3000 });
+
+wss.on('connection', function connection(ws) {
+  ws.on('message', function incoming(message) {
+  });
+
+});
+```
+
+[Thor](https://github.com/observing/thor) is used to run the benchmark.
+
+`thor -A 10000 http://localhost:3000`
+
+| Platform | CPU Usage | Memory Usage |
+| :------------ |:---------------:| -----:|
+| Crystal (Kemal)    | 1.85 | 11.2 MB  |
+| Node.js (ws)     | 38.95        |   906.3 MB |
+
+This benchmark was performed on a 2013 Late Macbook Pro with 2Ghz i7 and 8G ram.
+
+P.S: Less is better