chore(docs): Adds Android manual linking

Author: rommyarb

docs/Linking.md

@@ -2,4 +2,38 @@
 
 ## iOS
 
-## Android
+## Android
+1. Add project to `android/settings.gradle`:
+```diff
+rootProject.name = 'MyApp'
+
+include ':app'
+
++ include ':@react-native-community_async-storage'
++ project(':@react-native-community_async-storage').projectDir = new File(rootProject.projectDir, '../node_modules/@react-native-community/async-storage/android')
+  ```
+
+2. In `android/app/build.gradle` add to dependencies:
+```diff
+dependencies {
+  ...
++ implementation project(':@react-native-community_async-storage')
+}
+  ```
+
+3. Then, in `MainApplication.java`:
+```diff
+package com.myapp;
+
++ import com.reactnativecommunity.asyncstorage.AsyncStoragePackage;
+
+...
+
+@Override
+protected List<ReactPackage> getPackages() {
+    return Arrays.<ReactPackage>asList(
+        new MainReactPackage(),
++       new AsyncStoragePackage()
+    );
+}
+```