Add documentation for the `.xcode-version` file by rogerluan · Pull Request #218 · XcodesOrg/xcodes

Ooh. Interesting! This makes sense.
Maybe this should be made more explicit to users, perhaps? For instance, when printing xcodes list, we see this:

[…]
13.0 Beta (13A5154h)
13.0 Beta 2 (13A5155e)
13.0 Beta 3 (13A5192i)
13.0 Beta 3 (13A5192j)
13.0 Beta 4 (13A5201i)
13.0 Beta 5 (13A5212g)
13.0 (13A233)
13.1 (13A1030d)
13.2 Beta (13C5066c)
13.2 Beta 2 (13C5081f)
13.2 (13C90)
13.2.1 (13C100)
13.3 Beta (13E5086k)
13.3 Beta 2 (13E5095k)
13.3 Beta 3 (13E5104i)
13.3 (13E113)
13.3.1 (13E500a)
13.4 (13F17a)
13.4.1 (13F100) (Installed)
14.0 Beta (14A5228q)
14.0 Beta 2 (14A5229c)
14.0 Beta 3 (14A5270f)
14.0 Beta 4 (14A5284g)
14.0 Beta 5 (14A5294e)
14.0 Beta 6 (14A5294g)
14.0 (14A309) (Installed, Selected)
14.1 Beta (14B5024h) (Installed)
14.0.1 Release Candidate (14A400)

So it's not clear how one should guess what the identifier for those betas and RCs should be, if they are not aware of that rule (e.g. "14.1b1"), what do you think?

Of course, this ☝️ is unrelated to this PR, and I can update this PR to reflect the current logic, but just some food for thought for another future improvement :)