[Bf-docboard] guidelines for wiki.blender.org

[Tom M]

Ton recently asked me if we had any posted guidelines about what is
and isn't appropriate for blender.org, and if not he would like us to
do so.

In particular he would like it to be clear that content only directly
and clearly related to blender should be hosted there, and other
content only tangentially related should be hosted elsewhere.

Ie so content on using blender is good, but broader animation and
technical information should probably go elsewhere.

LetterRip