[Android docs] Add maven part

Now user can also add executorch android lib as a maven dependency.

Author: kirklandsign

docs/source/using-executorch-android.md

@@ -6,7 +6,7 @@ Note: This page covers Android app integration through the AAR library. The Exec
 
 ## Installation
 
-All ExecuTorch Android libraries are packaged into an Android library (AAR), `executorch.aar` for both generic (image/audio processing) and LLM (LLaMA) use case. In each release, prebuilt AAR artifacts are uploaded to S3. Users can also build the AAR from source.
+All ExecuTorch Android libraries are packaged into an [Android library (AAR)](https://developer.android.com/studio/projects/android-library), `executorch.aar` for both generic (image/audio processing) and LLM (LLaMA) use case. In each release, prebuilt AAR artifacts are uploaded to [Maven](https://repo.maven.apache.org/maven2/org/pytorch/executorch-android/) and S3. Users can also build the AAR from source.
 
 ### Contents of library
 
@@ -22,7 +22,21 @@ The AAR artifact contains the Java library for users to integrate with their Jav
   - LLaMa-specific Custom ops library.
 - Comes with two ABI variants, arm64-v8a and x86\_64.
 
-## Downloading AAR
+## Using AAR from Maven Central
+
+Simply add the following `org.pytorch:executorch-android` to your Android app dependency (build.gradle), and build your app.
+
+For example:
+```
+# app/build.gradle.kts
+dependencies {
+    implementation("org.pytorch:executorch-android:0.5.1")
+}
+```
+
+## Using AAR file directly
+
+You can also directly specify an AAR file in the app. We upload pre-built AAR to S3 during each release, or as a snapshot.
 
 ### Released versions (recommended)
 
@@ -36,13 +50,13 @@ The AAR artifact contains the Java library for users to integrate with their Jav
 | ------- | --- | ------- |
 | 2025-02-27 | [executorch.aar](https://ossci-android.s3.amazonaws.com/executorch/release/executorch-20250227/executorch.aar) | [executorch.aar.sha256sums](https://ossci-android.s3.amazonaws.com/executorch/release/executorch-20250227/executorch.aar.sha256sums) |
 
-## Using prebuilt libraries
+## Using AAR file
 
-To add the Java library to your app:
+To add the AAR file to your app:
 1. Download the AAR.
 2. Add it to your gradle build rule as a file path.
 
-An AAR file itself does not contain dependency info. The Java package requires `fbjni` and `soloader`, and currently requires users to explicitly declare the dependency. Therefore, two more `dependencies` in gradle rule is required:
+An AAR file itself does not contain dependency info, unlike the Maven one which bundled with pom.xml. The Java package requires `fbjni` and `soloader`, and currently requires users to explicitly declare the dependency. Therefore, two more `dependencies` in gradle rule is required:
 ```
 implementation("com.facebook.soloader:soloader:0.10.5")
 implementation("com.facebook.fbjni:fbjni:0.5.1")
@@ -58,7 +72,7 @@ curl https://ossci-android.s3.amazonaws.com/executorch/release/v0.5.0-rc3/execut
 
 And include it in gradle:
 ```
-# app/build.grardle.kts
+# app/build.gradle.kts
 dependencies {
     implementation(files("libs/executorch.aar"))
     implementation("com.facebook.soloader:soloader:0.10.5")
@@ -77,9 +91,10 @@ You need Android [SDK](https://developer.android.com/studio) and [NDK](https://d
 
 Current NDK version used in ExecuTorch CI: r27b.
 
-You need to set `ANDROID_NDK` to the correct NDK root (containing NOTICE file).
+You need to set `ANDROID_HOME` to Android SDK home and `ANDROID_NDK` to the correct NDK root (containing NOTICE file).
 
 ```
+export ANDROID_HOME=/path/to/sdk
 export ANDROID_NDK=/path/to/ndk
 sh build/build_android_library.sh
 ```