Hi,
Chad and Jeremy - thanks for your help.
I tried my hand at improving the documentation by adding a "Downloading skins" section - you can see the result here:
https://www.mediawiki.org/wiki/Manual:Skin_configuration
This documentation is probably still not complete - for instance, I wasn't sure if there was a way to download a skin other than via Git. Anyone should feel free to modify the page further, of course.
-Yaron