Added single-server to readme (#390)

<!-- INSTRUCTION: Keep the line below to notify all core developers about this new PR -->
@RocketChat/ReactNative

<!-- INSTRUCTION: Inform the issue number that this PR closes, or remove the line below -->
Closes #386 
Closes #295 

<!-- INSTRUCTION: Tell us more about your PR with screen shots if you can -->

README.md

@@ -44,6 +44,11 @@ Follow the [React Native Getting Started Guide](https://facebook.github.io/react
     $ npm run android
     ```
 
+# Running single server
+If you don't need multiple servers, there is a branch `single-server` just for that.
+
+Readme will guide you on how to config.
+
 # Detox (end-to-end tests)
 - Build your app