When no skins are enabled the MediaWiki installer provides instructions of how to enable skins
This is currently flawed as the MinervaNeue skin, although named MinervaNeue, actually uses the internal key "minerva" (see related T173546)
It's also possible for a skin repo to provide multiple skins
Ideally, skin.json for each skin should be loaded and parsed to extract ValidSkinNames - and this should be used to provide information.
This also allows for skin.json to provide more metadata in future - for instance a screenshot.