Added a page on Branding

1 new page with a brief description of recommended use of the terms and
logos plus a link to it is the site navigation.
Python.org has a "python logo" link in the footer of their landing page (which is actually a site map). So that's one. Its a different because they are in a better position legally speaking, with their branding.

You make it sound like you think the dlang.org is something put together for outsiders and all the community activity goes on elsewhere. I think dlang.org should face both ways, and so it is the perfect place for a document like this.