GO DOWNLOAD MY CAT HERE:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=3020285959
(i swear this is a required part of the guide)

go find the mod folder, should be something like below:
C:\Program Files (x86)\Steam\steamapps\common\Cookie Clicker\resources\app\mods\workshop

alternatively you can open the mod menu in game and open up the mod folder

copy the OliveTheCookie folder to the local mods folder, mine is
C:\Program Files (x86)\Steam\steamapps\common\Cookie Clicker\resources\app\mods\local

• rename the mod folder to whatever you want
  
• open the folder, place images of your cat, make a round one and name it cookie.png or something
  
• add another called thumbnail.png i guess
  
• oh yeah go get notepad++ btw
  
• with notepad++, open up both info.txt and main.js

change the following bits:

• name to whatever you like
  
• id to a string you like, i picked olivethecookie
  
• author and description should be obvious
  
• you can leave modversion and gameversion
  
• make the date current i guess
  
• leave dependencies and disabled as is
  
• take the , off the end of allowsteamachievs
  
• finally, delete the entire line of workshop

YOU'RE SO CLOSE, I'M SO PROUD OF YOU!!!

• in the brackets next to game.registermod, change olivethecookie to the ID you picked in info.txt
  
• now just replace olive.png with the name of your file

• reload your game, open mods menu (options>mods>manage mods)
  
• simply click your new kitty mod and enable

let me know if this guide sucks or needs more info.
if you upload your mod to the workshop please credit this fantastic kitty mod that started it all:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2990321549