Bug#987206: Mention GitHub on copyright page

[積丹尼 Dan Jacobson]

Package: libxml-libxml-perl
Version: 2.0134+dfsg-2+b1
Severity: wishlist
File: /usr/share/doc/libxml-libxml-perl/copyright

Perhaps mention
https://github.com/shlomif/perl-XML-LibXML/issues
on /usr/share/doc/libxml-libxml-perl/copyright .