Include example for pre-releases in Git checker

[TheEvilSkeleton]

The example we see in https://github.com/flathub/flatpak-external-data-checker/#git-checker is only for stable releases, right?

If it is, can you include an option for pre-releases too? Maybe even latest release while ignoring stable or pre-relase?

[gasinvein]

GitChecker is for git tags, it doesn't know anything about releases. If you want to track Github/Gitlab releases, use JSONChecker instead.