Update the README file to be more descriptive.

Author: dajhorn

README

@@ -1,4 +1,12 @@
-An alternative implementation of the zfs-auto-snapshot service for Linux.
+zfs-auto-snapshot:
+
+An alternative implementation of the zfs-auto-snapshot service for Linux
+that is compatible with zfs-linux and zfs-fuse.
+
+Automatically create, rotate, and destroy periodic ZFS snapshots. This is
+the utility that creates the @zfs-auto-snap_frequent, @zfs-auto-snap_hourly,
+@zfs-auto-snap_daily, @zfs-auto-snap_weekly, and @zfs-auto-snap_monthly
+snapshots if it is installed.
 
 This program is a posixly correct bourne shell script.  It depends only on
 the zfs utilities and cron, and can run in the dash shell.