add missing file remove routine "unlink"

doc/Language/io.pod6

@@ -110,11 +110,11 @@ To explicitly write binary data to a file, open it with the C<:bin> option.
 The input/output operations then will take place using the C<Buf> type instead
 of the C<Str> type.
 
-=head1 Copying and renaming files
+=head1 Copying, renaming, and removing files
 
-Routines C<copy>, C<rename>, and C<move> are available to avoid low-level system
-commands. See details at L<copy|/routine/copy>, L<rename|/routine/rename>, and
-L<move|/routine/move>. Some examples:
+Routines C<copy>, C<rename>, C<move>, and C<unlink> are available to avoid low-level system
+commands. See details at L<copy|/routine/copy>, L<rename|/routine/rename>,
+L<move|/routine/move>, and C<unlink|/routine/unlink>. Some examples:
 
 =begin code
 my $filea = 'foo';
@@ -131,6 +131,10 @@ rename $filea, 'new-foo', :createonly; # fails if 'new-foo' exists
 # use move when a system-level rename may not work
 move $fileb, '/disk2/foo';              # overwrites '/disk2/foo' if it exists
 move $fileb, '/disk2/foo', :createonly; # fails if '/disk2/foo' exists
+
+unlink $filea;    # removes $filea
+$fileb.IO.unlink; # removes $fileb
+
 =end code
 
 =head1 Checking files and directories