Update links to use current docs site

[danielhoherd]

Update docs links. The old docs links point to a site that appears to be RTD style boilerplate.

[gemini-code-assist]

Code Review

This pull request correctly updates outdated documentation links for libostree. I've suggested a minor improvement to point the links directly to their final destination URL to avoid redirects. While reviewing, I also noticed that a Dockerfile in experiments-and-demos uses a very old, unsupported Fedora version, and a link to 'Project Atomic' in the documentation points to an archived project. It would be beneficial to address these in a future PR.

[cgwalters]

Thank you!