* Test with `podman` and add according instructions
* Allow use of a custom `pacman.config`/`makepkg.config` by mounting them
into a special directory within the container
* Add my GPG key to the pacman keyring (not nice to hard-code it in the
Dockerfile but good enough for now)
* Install ccache into the base image to support makepkg's ccache option
* Split syncing packages and execution of `makepkg` so syncing can be
avoided when only building source package
* Don't quote `CRE`, it is unlikely spaces are needed here and using
chained commands (e.g. `sudo …`) might be useful
* Add documentation
