Allow fd.o to join forces with X.Org

The leadership of freedesktop.org (fd.o) has recently expressed interest
in having an elected governing body. Given the tight connection between
fd.o and X.Org and the fact that X.Org has such a governing body it
seemed obvious to consider extending X.Org's mandate to fd.o.

Quite a bit of background on fd.o leading up to this has been covered by
Daniel Stone at XDC 2018 [2] and was covered really well by Jake Edge of
LWN [1].

One question that is briefly addressed in the LWN article and was
thoroughly discussed by members of the X.Org boards, Daniel Stone, and
others in hallway discussions is the question of whether to extend the
X.Org membership to projects hosted on fd.o but outside the purpose of
the X.Org foundation as enacted in its bylaws.

Most people I talked to would prefer not to dilute X.Org's mission and
extend membership only to contributors of projects that follow X.Org's
purpose as enacted in its bylaws. Other projects can continue to be
hosted on fd.o but won't receive X.Org membership for the mere reason of
being hosted on fd.o.

[1] https://lwn.net/Articles/767258/
[2] https://youtu.be/s22B3E7rUTs



v3:
 - Clarify what support of fd.o projects entails without formalizing a
   two-tier system for fd.o projects that fall under X.Org's mandate and
   those who don't
 - Add link to Daniel's talk at XDC2018

v2:
 - Subject line that better describes the intention
 - Briefly describe reasons behind this change
 - Drop expanding membership eligibility

Acked-by: Daniel Stone <daniel@fooishbar.org>