📝 added websockets doc page #2506

* Simple explanation.
* Example of usage with JS.
* Additional nGinx config example.

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 +1,32 @@
+.. _websocket:
+
+=========
+Websocket
+=========
+
+You can enable web sockets if you select ``use_async`` option when creating a project. That indicates whether the project should 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 are using nGinx instead of Traefik, you should add these lines to nGinx config: ::
+
+    location /websocket/ {
+        proxy_pass http://backend;
+        proxy_http_version 1.1;
+        proxy_set_header Upgrade $http_upgrade;
+        proxy_set_header Connection "upgrade";
+        proxy_read_timeout 86400;
+    }
+
+Source: https://www.nginx.com/blog/websocket-nginx/