Add new websockets doc page

docs/index.rst

@@ -23,6 +23,7 @@ Contents:
    deployment-on-heroku
    deployment-with-docker
    docker-postgres-backups
+   websocket
    faq
    troubleshooting
 

docs/websocket.rst

@@ -0,0 +1,25 @@
+.. _websocket:
+
+=========
+Websocket
+=========
+
+You can enable web sockets if you select ``use_async`` option when creating a project. That indicates whether the project can use web sockets with Uvicorn + Gunicorn.
+
+Usage
+-----
+
+JavaScript example: ::
+
+    > ws = new WebSocket('ws://localhost:8000/') // or 'wss://<mydomain.com>/' in prod
+    WebSocket {url: "ws://localhost:8000/", readyState: 0, bufferedAmount: 0, onopen: null, onerror: null, …}
+    > ws.onmessage = event => console.log(event.data)
+    event => console.log(event.data)
+    > ws.send("ping")
+    undefined
+    pong!
+
+
+If you don't use Traefik, you might have to configure your reverse proxy accordingly (example with Nginx_).
+
+.. _Nginx: https://www.nginx.com/blog/websocket-nginx/