I never really used IRC, but in my experience contributing to projects which use mailing lists is very easy - you just send a mail with some code.

Of course you could use git-send-email, and you could create diffs and patches, but I actually think for a new contributor the mailing list workflow is the simplest since it doesn’t actually require knowledge of the various tools experienced developers use.

I write this from personal experience BTW - the first projects I contributed to used mailing lists, which allowed me to contribute even as a self taught programmer who had no experience with any VCS yet.