It's VERY simple. You don't have to add anything.
Place ESF-Bot.dll in your ESF/dlls folder, then go back to your ESF folder (main), open the file liblist.gam using NotePad, remove the // infront of gamedll "dlls\ESF-Bot.dll" and put // infront of gamedll "dlls\hl.dll", then save. Then open your config.cfg file (Found in the same folder - ESF) with NotePad, find console "0" and change it to console "1" (If it already is set to 1, don't worry about it), save.
Then, if you haven't done so already, make a shortcut (or copy one that you use for another Half-Life mod), and add -console -game ESF -numericpings to the TARGET line (Remove Any Other -game ModName entries). Re/Name the shortcut to ESF and use it to play ESF, & that's it.
When you are in the game, bring down console Tilde Key ~, and type addbot CharacterName BotName (Example: addbot Cell Mr.Bot)