These are my notes I kept for future reference once I got the extension installed and up and running in the game I've just finished. I'm going to have to set it all up again for the next project so I wrote down the important information.
To install Neko after you have downloaded it you need to cd to its path and use: "brew --prefix neko"
This should also put the neko binary into the $PATH and stop having to security exception it. You'll probably need to enter your login password here.
If you get an error after installing then also try this, as it worked for me then.
"brew reinstall neko"
Navigate to the projects datafiles/GMLive folder then select neko and press CMD/Shift/R to open terminal in that folder.
Type in "neko gmlive-server.n"