DocBook schema tracker now on GitHub

[Bob Stayton <bobs@sagehill.net>]

As part of our efforts to transition from SourceForge to GitHub, we have 
moved the issues tracker for requests for DocBook schema changes to 
GitHub at:

https://github.com/docbook/docbook/issues

The old one on SourceForge will no longer accept new requests, and we 
have copied any active RFEs from there to GitHub.

--
Bob Stayton
Sagehill Enterprises
bobs@sagehill.net