Though homepage is rendered completely from a template,
it still needs an index.md to generate.
Also change subpage breadcrumb links to relative, so they
work in the GitHub Pages context. For example "/" points
to the Google Org's home rather than Draco's home, so use
"..", etc.
GitHub is configured to use the contents of `/docs` for web
content, thus treating `docs` as the docroot, thus configuring
a baseurl of `/docs` is mistaken in production (GitHub Pages).
In the local dev case a baseurl is needed (`/docs`), but can
be passed on the Jekyll commandline.
