Correct doc/patch.mdwn documentation: tag -> link.

[ikiwiki] / doc / bugs / Undefined_subroutine_IkiWiki::refresh.mdwn

After building a fresh deb from current Git master (9b62dac4bcf62f3a1f76ec5a7ed5a90db16ea1c8) :

        $ ikiwiki --setup ~/ikiwiki.setup  --rebuild
        Undefined subroutine &IkiWiki::refresh called at /usr/share/perl5/IkiWiki/Setup.pm line 113.

> [[done]], it just needed "require IkiWiki::Render" before it started
> rendering. --[[smcv]]