Updated AsciiDoc brand guideline available

The AsciiDoc brand guidelines have been updated in support of our logo registration efforts. The updated guidelines are hosted on https://www.eclipse.org/org/artwork/. If the guidelines are required on any other sites/repo, please provide the direct link to https://www.eclipse.org/org/artwork/guidelines/asciidoc-brand-guidelines.pdf

CC @scorbett @mkokabi