Update README.md

Add section about websocket authorization

README.md

@@ -81,6 +81,14 @@ matchengine
 
 [HTTP Protocl](https://github.com/viabtc/viabtc_exchange_server/wiki/HTTP-Protocol) and [Websocket Protocl](https://github.com/viabtc/viabtc_exchange_server/wiki/WebSocket-Protocol) documents are available in Chinese. Should time permit, we will have it translated into English in the future.
 
+## Websocket authorization
+
+The websocket protocol has an authorization method (`server.auth`) which is used to authorize the websocket connection to subscribe to user specific events (trade and balance events).
+
+To accomodate this method your exchange frontend will need to supply an internal endpoint which takes an authorization token from the HTTP header named `Authorization` and validates that token and returns the user_id.
+
+Example response: `{"code": 0, "message": null, "data": {"user_id": 1}}`
+
 ## Donation
 
 * BTC: 14x3GrEoMLituT6vF2wcEbqMAxCvt2724s