Bots are already included in the game Counter-Strike:Source. If you want to have these on your server, you will need to enter a couple of commands in server.cfg. If you want to have bots with us, you will need the corresponding option in your tariff. You can also do this retroactively with a tariff change.

bot_quota "number"  
The number of bots that join the server when the server is started.

bot_prefix "tag"            
Sets a clan tag before each bot name.

bot_join_after_player 0/1        
If this option is active, the bots only appear once a player is on the server.