troubleshooting docs (clone #14885)

Summary:
I added troubleshooting docs for connection to the development server from device, otherwise it's maybe hard to find out why it's not working.

Due to a disparity in what GitHub's API return the original PR (https://github.com/facebook/react-native/pull/14885) couldn't get imported, so I created a new PR as hramos suggested.
Closes https://github.com/facebook/react-native/pull/15304

Differential Revision: D5537615

Pulled By: hramos

fbshipit-source-id: b94e887b1b771be9e93854124bd0a56b27fd0097

docs/RunningOnDevice.md

@@ -237,8 +237,44 @@ You can also iterate quickly on a device using the development server. You only
 
 ![](img/DeveloperMenu.png)
 
+### Troubleshooting
+
 > If you have any issues, ensure that your Mac and device are on the same network and can reach each other. Many open wireless networks with captive portals are configured to prevent devices from reaching other devices on the network. You may use your device's Personal Hotspot feature in this case.
 
+When trying to connect to the development server you might get a [red screen with an error](docs/debugging.html#in-app-errors-and-warnings) saying:
+> Connection to [http://localhost:8081/debugger-proxy?role=client]() timed out. Are you running node proxy? If you are running on the device, check if you have the right IP address in `RCTWebSocketExecutor.m`.
+
+To solve this issue check the following points.
+
+#### 1. Wi-Fi network.
+
+Make sure your laptop and your phone are on the **same** Wi-Fi network.
+
+#### 2. IP address
+
+Make sure that the build script detected the IP address of your machine correctly (e.g. 10.0.1.123). 
+
+![](img/XcodeBuildIP.png)
+
+Open the **Report navigator** tab, select the last **Build** and search for `xip.io`. The IP address which gets embedded in the app should match your machines IP address plus the domain `.xip.io` (e.g. 10.0.1.123.xip.io)
+
+#### 3. Network/router configuration
+
+React Native uses the wildcard DNS service **xip.io** to address your device. Some routers have security features to prevent DNS Servers to resolve anything in the local IP range.
+
+Now check if you are able to resolve the xip.io address, by running `nslookup`.
+
+```bash
+$ nslookup 10.0.1.123.xip.io
+```
+
+If it doesn't resolve your local IP address either the **xip.io** service is down or more likely your router prevents it. 
+
+To still use xip.io behind your rooter:
+
+- configure your phone to use Google DNS (8.8.8.8)
+- disable the appropriate security feature in your router
+
 <block class="mac windows linux android" />
 
 ## Connecting to the development server