CNCF provides the Kubernetes artwork in a number of standard formats
with the text and logo integrated. Note that we're not deleting the old
artwork in case other sites are relying on it.
Move all log-related files to a logo/ dir.
Add a logo with the white border (common for dark backgrounds).
Add a rendered image of the name in the 'ubuntu' font.
Update usage guidelines:
- new links
- linewraps
- typos