Update flask docs to add ratelimiting checks

docs/flask.md

@@ -33,6 +33,19 @@ AIKIDO_BLOCKING=true
 
 It's recommended to enable this on your staging environment for a considerable amount of time before enabling it on your production environment (e.g. one week).
 
+## Rate limiting and user blocking
+If you want to add the rate limiting feature to your app, modify your code like this:
+```py
+from aikido_zen.middleware import AikidoFlaskMiddleware
+
+app = Flask(__name__)
+# ...
+app.wsgi_app = AikidoFlaskMiddleware(app.wsgi_app)
+# ...
+# set user in middleware
+# ...
+```
+
 ## Debug mode
 
 If you need to debug the firewall, you can run your code with the environment variable `AIKIDO_DEBUG` set to `true`: