This PR should be merged after the new website is deployed.
- [x] Rename files
- [x] Add front matter section to all `.md` files in the book (necessary for Zola)
- [x] Change all internal links to use Zola's linking system that checks broken links
- [x] Some updates to documentation contents and organization
Co-authored-by: Alex Auvolat <alex@adnab.me>
Reviewed-on: Deuxfleurs/garage#213
Co-authored-by: Alex <alex@adnab.me>
Co-committed-by: Alex <alex@adnab.me>
