Documentation Updates

docs/messaging/android.md

@@ -8,4 +8,51 @@ description: Manually integrate Messaging into your Android application.
 > The following steps are only required if your environment does not have access to React Native
 > auto-linking.
 
-## TODO
+#### Update Gradle Settings
+
+Add the following to your projects `/android/settings.gradle` file:
+
+```groovy
+include ':@react-native-firebase_messaging'
+project(':@react-native-firebase_messaging').projectDir = new File(rootProject.projectDir, './../node_modules/@react-native-firebase/messaging/android')
+```
+
+#### Update Gradle Dependencies
+
+Add the React Native Functions module dependency to your `/android/app/build.gradle` file:
+
+```groovy{3}
+dependencies {
+  ...
+  implementation project(path: ":@react-native-firebase_messaging")
+}
+```
+
+#### Add package to the Android Application
+
+Import and apply the React Native Firebase module package to your `/android/app/src/main/java/**/MainApplication.java` file:
+
+Import the package:
+
+```java
+import io.invertase.firebase.messaging.ReactNativeFirebaseMessagingPackage;
+```
+
+Add the package to the registry:
+
+```java{4}
+protected List<ReactPackage> getPackages() {
+  return Arrays.asList(
+    new MainReactPackage(),
+    new ReactNativeFirebaseMessagingPackage(),
+```
+
+#### Rebuild the project
+
+Once the above steps have been completed, rebuild your Android project:
+
+```bash
+react-native run-android
+```
+
+