Adds another sentence clarifying behavior of unlink

Also some possible explanation of the rationale of including
non-existing files in the output list. Refs #2096, does not close,
because it's been closed already. Thanks again @briandfoy for the
report, and sorry for not understanding the problem from the beginning.

doc/Type/IO/Path.pod6

@@ -1009,10 +1009,15 @@ Defined as:
 Delete all specified ordinary files, links, or symbolic links for which there
 are privileges to do so. See L<rmdir> to delete directories.
 
-The subroutine form returns the names of the files that were successfully
-deleted. The method form returns C<True> on success, or L<fails|/routine/fail>
-with L<X::IO::Unlink> if the operation could not be completed. If the file
-to be deleted does not exist, the routine treats it as success.
+The subroutine form returns the names of all files, excluding those that exist,
+but could not be deleted; this obviously includes the names of the files that do
+not exist, the rationaly possibly being that it returns the names of the files
+that C<do not exist> after the operation, without taking into account if they
+existed before the operation or not.
+
+The method form returns C<True> on success, or L<fails|/routine/fail>
+with L<X::IO::Unlink> if the operation could not be completed. If the file to be
+deleted does not exist, the routine treats it as success.
 
 =begin code
 'foo.txt'.IO.open(:w).close;