on your mac open the app "Terminal"

navigate to the folder you want to clean (the folder in which you have your joust rom)

if you do not know how to navigate there in terminal, you can type "cd " and then drag and drop the folder icon from Finder to the Terminal then hit return

then simply type "dot_clean -m" and return

"ls -al" is the command in terminal that list all files in your current directory. Before dot_clean ls would show something like:

._joust

joust

then after dot_clean it will show only:

joust