Update deep-linking.md

Author: brentvatne

docs/deep-linking.md

@@ -31,7 +31,7 @@ const SimpleApp = createAppContainer(createStackNavigator({
 
 ## Set up with Expo projects
 
-You need to specify a scheme for your app. You can register for a scheme in your `app.json` by adding a string under the scheme key:
+First, you will want to specify a url scheme for your app. This corresponds to the string before `://` in a url, so if your scheme is `mychat` then a link to your app would be `mychat://`. The scheme only applies to standalone apps and you need to re-build the standalone app for the change to take effect. In the Expo client app you can deep link using `exp://ADDRESS:PORT` where `ADDRESS` is often `127.0.0.1` and `PORT` is often `19000` - the URL is printed when you run `expo start`. If you want to test with your custom scheme you will need to run `expo build:ios -t simulator` or `expo build:android` and install the resulting binaries in your emulators. You can register for a scheme in your `app.json` by adding a string under the scheme key:
 
 ```json
 {
@@ -41,33 +41,36 @@ You need to specify a scheme for your app. You can register for a scheme in your
 }
 ```
 
+
 ### URI Prefix
 
 Next, let's configure our navigation container to extract the path from the app's incoming URI. 
 
 ```js
+import * as Expo from 'expo';
+
 const SimpleApp = createAppContainer(createStackNavigator({...}));
 
 const prefix = Expo.Linking.makeUrl('/');
 
 const MainApp = () => <SimpleApp uriPrefix={prefix} />;
 ```
 
-### iOS
+The reason that is necessary to use `Expo.Linking.makeUrl` is that the scheme will differ depending on whether you're in the client app or in a standalone app.
+
+### Test deep linking on iOS
 
-To test the URI on the simulator (Expo client app ), run the following:
+To test the URI on the simulator in the Expo client app, run the following:
 
 ```
 xcrun simctl openurl booted [ put your URI prefix in here ]
 
 // for example
 
-xcrun simctl openurl booted exp://127.0.0.1:19004/--/chat/Eric
-
+xcrun simctl openurl booted exp://127.0.0.1:19000/--/chat/Eric
 ```
 
-
-### Android
+### Test deep linking on Android
 
 To test the intent handling in Android (Expo client app ), run the following:
 
@@ -76,8 +79,7 @@ adb shell am start -W -a android.intent.action.VIEW -d "[ put your URI prefix in
 
 // for example
 
-adb shell am start -W -a android.intent.action.VIEW -d "exp://127.0.0.1:19004/--/chat/Eric" com.simpleapp
-
+adb shell am start -W -a android.intent.action.VIEW -d "exp://127.0.0.1:19000/--/chat/Eric" com.simpleapp
 ```
 
 Read the [Expo linking guide](https://docs.expo.io/versions/latest/guides/linking.html) for more information about how to configure linking in projects built with Expo.