added link to AR library on JCentral

Author: codeanticode

README.md

@@ -3,11 +3,13 @@ Processing for Android
 
 This is the main repository for Processing for Android. It includes the core library inside the core folder, and the mode itself in the root. See the [wiki](https://github.com/processing/processing-android/wiki) for build instructions.
 
-The core and VR libraries are available on JCentral, so they can be easily imported
+The core, VR, and AR libraries are available on JCentral, so they can be easily imported
 into Gradle projects:
 
 [processing-core](https://bintray.com/p5android/processing-android/processing-core)
 
 [processing-vr](https://bintray.com/p5android/processing-android/processing-vr)
 
+[processing-ar](https://bintray.com/p5android/processing-android/processing-ar)
+