Hi! There should be a manual in the docs folder.
As for altars, you sacrifice items on them. Generally corpses, but other valuable items should work too. I'm pretty sure you can identify by dropping items on altars. If you're illiterate, praying might uncurse any cursed items you've got equipped.
There's not a lot of differences between the deities right now. They're underdeveloped, and a long way from eg DCSS. Key stats for witchlings are I think int/will/cha, and the Magic skill as well as Primordial and Cantrips.
Thieves don't start with Literacy. Some races do, so if you play a thief of one of those races, you should be good.