Option to add a custom label to all GitHub imported issues

[GoogleCodeExporter]

Due to the poor quality of issues imported in GitHub (See #28), could you add 
an option to the GitHub importer script to tag all the issues that were 
imported with a custom tag?
That would at least allow users browsing issues on GitHub to understand why 
they were all raised by/commented on by the repository owner and nobody else, 
if all issues were tagged with "Imported-From-GoogleCode" or something.

Thanks.

Original issue reported on code.google.com by [email protected] on 14 Mar 2015 at 7:44