README should provide to wrapdb guide

[asmodehn]

An example of "how to use this" in the README would be useful for newcomers...

[benmkw]

I had the same issue and think it would be good to add a hint to every readme (at first I thought these repos were all empty because they use branches for the versions :D)

so this should be helpful https://mesonbuild.com/Using-the-WrapDB.html

[legeana]

That's a good point, thank you. I will update https://github.com/mesonbuild/mesonwrap/blob/master/mesonwrap/tools/repoinit.py#L32-L35

[benmkw]

thanks, sounds good 👍