This took me a while (hours) to figure out because so many people give such rubbish information about it..... You are in luck because I'm giving you the simplest, fool proof method of getting it...
Type in bot_add in the console bar to add one bot, to bring up the console, click this: `A few more tips:Type in bot_kick to allow all bots to quit game when you are playing.Type in bot_kill to kill...