paccache: Use more accurate --min-a/mtime description

.. taken from the --help message.

Thanks to Patrick Smits (@ps0) for reporting this. Fixes #5

Signed-off-by: Daniel M. Capella <polyzen@archlinux.org>

doc/paccache.8.txt

@@ -38,10 +38,12 @@ Options
 	Scan for packages for a specific architecture. Default is to scan for
 	all architectures.
 
-*\--min-atime <age>*::
-*\--min-mtime <age>*::
-	Only consider packages for removal with atime respectively mtime older than
-	specified. The age can be given as '10d', '1m', '1y', '1y1m' etc.
+*\--min-atime <time>*::
+*\--min-mtime <time>*::
+	Keep packages with an atime/mtime that is not older than the time given,
+	even if this means keeping more than specified through the '--keep' option.
+	Accepts arguments according to 'info "Date input formats"', e.g. '30 days
+	ago'.
 
 *-c, \--cachedir <dir>*::
 	Specify a different cache directory. This option can be used more than once.