Clearify copyright status of specification for DFSG compatibility.

[petterreinholdtsen]

Adding new section "Copying condition" lifted from <URL: https://wiki.debian.org/NonFreeIETFDocuments > to ensure the specification text follow the Debian Free Software Guidelines and can be distributed as part of programs in Debian outside the non-free set.

[glpatcern]

Thanks Petter! This looks fine to me, @lisad @thibmeu how would you consider this paragraph?
For some context, this came out today at the CS3 workshop's OCM session.

cc @mickenordin

[mickenordin]

I asked Andy Newton about this, and his reply was that it may be ok to add such a clause, since the authors have copyright and is simply granting the IETF a license. BUT, to be absolutely sure we are not causing an issue here, he said that we should probably run this by ipr@ietf.org, and in addition the templates for ID may not allow for it. So I will do that, and request feedback from the IETF people about this. Personally I see no issue with it, and I am all for granting additional explicitly open source style licenses if someone needs it.