Following instructions to manually install arduino IDE here
Reason for manual installation is because package manager has an older version of the plugin (10 months).
After placing it in ../Packages, I open ST3 and watch Finder. Initially, the folder extracted is named "Stino-new-stino". A folder is created at ../Packages/User/Stino with what seems to be options for the topmenu, and then the Stino-new-stino folder is deleted.
Tried to put extracted folder into ../Installed Packages, as well as ../Packages/User, but doesn't get detected.
Also noticed that my TomorrowTheme package got moved into my ../Packages/User/SublimeLinter.
I removed SublimeLinter and it still seems to be happening so I'm thinking it's an ST3 thing.
There was some funky beta code happening and had to remove package-metadata.json for it to stop deleting itself.