Okay after learning that some prefer how Steam handles Windows apps under Proton under Linux, I wanted to have that as an available option for Linux. So you will now find that as a launch option when starting the game.
It's a launch script for that Proton Mode, and after installing a whole bunch of Proton versions to test them out I realized how quickly you can run out of hard drive space doing that. I moved my Proton versions to a second hard drive, only for it to no longer detect it in my script...
So I made an interactive Proton Setup script you can now use to configure your system. You don't have to be too specific when specifying the mount point of your Proton installations, the script is fairly robust to figure it out (let me know if you run into any edge-cases). 
You can specify your preferred version, or leave it blank and it will prefer Experimental. But for whatever reason if you want to try use a specific Proton version it will use those settings. 
You will still need to download Proton itself on Steam and move it into that drive you want to set it up on, if it differs from a default installation. If you move JAMs to some random drive, it should scan that drive's Steam common folder for Proton versions too without having to specify it. Should work!
I set this up on a separate depot, so this should just remain static on the game now, when I make new versions I won't have to maintain these scripts.
This way at least you can set up your game without needing to use a text editor to change the files, and if I push out an update to the scripts it won't alter your config file either.
And of course, the native Linux build still is the primary launch option for Linux machines.