Describe the bug
I am attempting to use r2modman with the flatpak version of steam on linux. I can install mods but when I click "Start Modded" nothing happens.

To Reproduce
Steps to reproduce the behavior:

1. Go to r2modman
2. Click on "Start Modded" with a game
3. Observe the game not opening

Expected behavior
I expected the game to open from steam

Additional Context
I realize this might not be able to be resolved on the r2modman side, but providing instructions to get it working with flatpak steam would be helpful. It seems this might be because of the steam flatpak's sandbox. Perhaps instructions could be added somewhere on github?