Automate the building and testing process of BookmarkFS using the
builds.sr.ht service, to see whether it still works on:
- Debian, Arch Linux
* Typical GNU/Linux distros, either stable or cutting-edge.
- Alpine Linux
* Minimal non-GNU setup, notably BusyBox, TinyCC, musl and pdpmake.
- FreeBSD
* FreeBSD kernel and userland, including Clang and others.
