add a runshell script to the top of the app directory

This is mostly useful when you have adb with root access, to easily start the
git-annex environment in there.

standalone/android/runshell

@@ -49,6 +49,10 @@ buildtree () {
 	$cmd mkdir -p "$base/templates"
 	$cmd mkdir -p "$base/tmp"
 
+	echo "#!/system/bin/sh" > "$base/runshell"
+	echo "exec $base/lib/lib.start.so" >> "$base/runshell"
+	chmod 755 runshell
+
 	$cmd cat "$base/lib/lib.version.so" > "$base/installed-version"
 	$cmd echo "Installation complete"
 }