Support for Linux Steam Deck asset detection

Motivation

REQUEST MOTIVATION SteamOS (Based on Arch Linux) asset detection doesn't pick up Steam Deck paths (internal SSD or SD Card)

Proposed solution

PROPOSED SOLUTION Add the specific paths for SteamOS, or possibly a more generic "directory file picker"

Side effects

EXPECTED SIDE EFFECTS No ill side effects expected

Alternatives

ALTERNATIVES Manually creating Symlinks to where the OpenRA resources are expected to be