Update performance test README

performance/README.rst

@@ -24,7 +24,13 @@ Performance Tests
         }
     }
 
-4. Start the Locust server, and point it at the test server.  **NOTE**: You *must* include the trailing slash in the host URL.
+4. **Optional**: Increase open file limit:
+
+.. code:: bash
+
+    ulimit -n 2048
+
+5. Start the Locust server, and point it at the test server.  **NOTE**: You *must* include the trailing slash in the host URL.
 
 .. code:: bash
 
@@ -39,4 +45,4 @@ If your server has basic auth enabled, provide credentials with environment vars
     cd performance
     BASIC_AUTH_USER=foo BASIC_AUTH_PASSWORD=bar locust --host=http://example.com/
 
-5. Visit the `Locust web UI <http://localhost:8089>`_
+6. Visit the `Locust web UI <http://localhost:8089>`_ to start the test.