[Skiboot] gh-pages branch and docs

[Stewart Smith]

For those not aware, the gh-pages branch in the github skiboot
repository generates this web site:
https://open-power.github.io/skiboot/

Where there's bits and pieces (most notable the built documentation from
doc/)

I had been just adding commits onto the gh-pages branch, but it's likely
nobody actually cares about the history of autogenerated docs, so I've
just "git push -f"'d it to wipe out the history and save you all some MB
of disk space when git garbage collects.

-- 
Stewart Smith
OPAL Architect, IBM.