Add message to remind user to enable wifi

Summary:
Our iOS devs frequently turn off wifi and forget to turn it back on. This message should remind them that they need wifi to connect. Often they waste several minutes due to this problem.

I'm not sure if there's a test plan to apply here. Any suggestions?
Closes #13551

Differential Revision: D5149231

Pulled By: hramos

fbshipit-source-id: 0afc71024f10f802ac1a50435fb57fc10a02c819

React/Base/RCTJavaScriptLoader.mm

@@ -218,7 +218,8 @@ static void attemptAsynchronousLoadOfBundleAtURL(NSURL *scriptURL, RCTSourceLoad
                      [@"Could not connect to development server.\n\n"
                       "Ensure the following:\n"
                       "- Node server is running and available on the same network - run 'npm start' from react-native root\n"
-                      "- Node server URL is correctly set in AppDelegate\n\n"
+                      "- Node server URL is correctly set in AppDelegate\n"
+                      "- WiFi is enabled and connected to the same network as the Node Server\n\n"
                       "URL: " stringByAppendingString:scriptURL.absoluteString],
                    NSLocalizedFailureReasonErrorKey: error.localizedDescription,
                    NSUnderlyingErrorKey: error,