Add deprecation notice.

README.md

@@ -4,12 +4,21 @@ adb-sync
 adb-sync is a tool to synchronize files between a PC and an Android device
 using the ADB (Android Debug Bridge).
 
+DEPRECATED
+==========
+
+This project is no longer being maintained; please use
+[better-adb-sync](https://github.com/SelfAdjointOperator/better-adb-sync)
+instead. Thanks!
+
 Related Projects
 ================
 
 Before getting used to this, please review this list of projects that are
 somehow related to adb-sync and may fulfill your needs better:
 
+* [better-adb-sync](https://github.com/SelfAdjointOperator/better-adb-sync) is
+  an improved rewrite of this project.
 * [rsync](http://rsync.samba.org/) is a file synchronization tool for local
   (including FUSE) file systems or SSH connections. This can be used even with
   Android devices if rooted or using an app like