Add note about --live-server-wait timeout into documentation

Author: vitalk

docs/features.rst

@@ -174,6 +174,12 @@ example, in your project’s ``pytest.ini`` file)::
             assert b'got it' in res.read()
 
 
+``--live-server-wait`` - the live server wait timeout (5 seconds)
+`````````````````````````````````````````````````````````````````
+
+The timeout after which test case is aborted if live server is not started.
+
+
 ``request_ctx`` - request context
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~