Merge pull request #4105 from davidv171/master

Show warning when using --backend with a running instance

qutebrowser/app.py

@@ -129,6 +129,9 @@ def run(args):
         sys.exit(usertypes.Exit.err_ipc)
 
     if server is None:
+        if args.backend is not None:
+            log.init.warning(
+                "Backend from the running instance will be used")
         sys.exit(usertypes.Exit.ok)
     else:
         server.got_args.connect(lambda args, target_arg, cwd: