Make a GNU FSDG hack of Debian Reference

From User Issue 5950 http://trisquel.info/en/issues/5950

The idea here is not to produce an edit of the quality of the original Debian Reference. But, to butcher whatever obviously isn't FSDG out of the document as there is much remaining which is interesting and useful. E.g. @aklis linked me an interesting section of it on IRC less than 24 hours ago.