Commit 5b9964c implements support for loading a Version field in pack data. How to actually display this will fall under the overall menu overhaul, so is beyond the scope of this topic.
If you want to prepare in advance, the format is:
VERSION 1.00 (replacing "1.00" with whatever version number you want)
In regard to how you select version numbers - it's up to you. Just keep it sane - ideally, if you were to make a list of all version numbers of your pack, and sort them alphanumerically, the resulting order would be oldest to newest.
V12.9.X and older will simply outright ignore this line, so while it won't be recognized by current versions, it won't do any harm either.