readme: ./xbps-src update-check

Author: uggedal

README.md

@@ -2,6 +2,6 @@ void-updates
 ============
 
 Script intended to be run daily via cron for finding upstream updates
-to [void-packages][].
+to [void-packages][]. This is just a wrapper around `./xbps-src update-check`.
 
 [void-packages]: https://github.com/voidlinux/void-packages