docs(*): move enabling multidex to root

Author: Ehesp

docs/enabling-multidex.md

@@ -0,0 +1,35 @@
+---
+title: Enabling Multidex
+description: Learn how to enable multidex on your Android application.
+---
+
+As more native dependencies are added to your project, it may bump you over the
+64k method limit on the Android build system. Once this limit has been reached, you will start to see the following error
+whilst attempting to build your Android application:
+
+```
+Execution failed for task ':app:mergeDexDebug'.
+```
+
+To learn more about multidex, view the offical [Android documentation](https://developer.android.com/studio/build/multidex#mdex-gradle).
+
+## Enabling Multidex
+
+Open the `/android/app/build.gradle` file. Under `dependencies` we need to add the module, and then enable it
+within out `defaultConfig`:
+
+```groovy
+android {
+    defaultConfig {
+        // ...
+        multiDexEnabled true
+    }
+    // ...
+}
+
+dependencies {
+  implementation 'com.android.support:multidex:1.0.3'
+}
+```
+
+Once added, rebuild your application: `npx react-native run-android`.

docs/firestore/enabling-multidex.md

@@ -25,8 +25,8 @@ cd ios/ && pod install
 If you're using an older version of React Native without autolinking support, or wish to integrate into an existing project,
 you can follow the manual installation steps for [iOS](/firestore/usage/installation/ios) and [Android](firestore/usage/installation/android).
 
-In some scenarios, your Android build may fail with the `app:mergeDexDebug` error. This required that multidex is enabled
-for your application. To learn more, read the [Enabling Multidex](/firestore/enabling-multidex) documentation.
+If you have started to receive a `app:mergeDexDebug` error after adding Cloud Firestore, please read the 
+[Enabling Multidex](/enabling-multidex) documentation for more information on how to resolve this error.
 
 # What does it do
 

docs/firestore/usage/index.md

@@ -156,6 +156,15 @@ you can follow the manual installation steps for [iOS](/install-ios) and [Androi
 
 # Miscellaneous
 
+## Android Enabling Multidex
+
+As your application starts to grow with more native dependencies, your builds may start to fail with the common
+`Execution failed for task ':app:mergeDexDebug'` error. This error occurs when Android reaches the
+[64k methods](https://developer.android.com/studio/build/multidex) limit.
+
+One common solution is to [enable multidex](/enabling-multidex) support for Android. This is a common solution to solving
+the problem, however it is recommended you read the Android documentation to understand how it may impact your application.
+
 ## Hermes Support
 
 At this time, React Native Firebase does not support the [Hermes](https://hermesengine.dev/) JavaScript engine due to