Coca-Cola: open up assets0.pk3 and find the botfiles folder. In there you will find various .jkb files which control bot personality, as well as one bots.txt folder that lists model information about the bot. The bots.txt file entries control which bots will be added to your server automatically in accordance with bot_minplayers, and the .jkb files store the personality that each entry for a bot in bots.txt references.
Really, open up assets0.pk3 and look at how it's set up in the botfiles folder, you can find plenty of examples in it.