Clarify behaviour of unlink on non-existent files

Closes #2096 D#2096

doc/Type/IO/Path.pod6

@@ -1011,7 +1011,20 @@ 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.
+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;
+'bar'.IO.mkdir;
+say unlink <foo.txt  bar  not-there.txt>; # OUTPUT: «[foo.txt not-there.txt]␤»
+# `bar` is not in output because it failed to delete (it's a directory)
+# `not-there.txt` is present. It never existed, so that's deemed a success.
+
+# Method form `fail`s:
+say .exception.message without 'bar'.IO.unlink;
+# OUTPUT: «Failed to remove the file […] illegal operation on a directory␤»
+=end
 
 =head2 method IO