Fixes for Manjaro Linux

[thesecretsauce67420]

What this does is above

[programmer1o1]

I checked this, and uh there are some problems here:

1. Manjaro Steam path (~/.steam/manjaro-installation)
   IIRC, steam linux directory is usually on ~/.local/share/Steam, ~/.steam/steam, and ~/.steam/root on Arch (which Manjaro is based on) and even Manjaro as well. These are all standard paths.

2. Model path change (models/srcbox.mdl)
   This changes models/props/srcbox/srcbox.mdl → models/srcbox.mdl in two places, but the rest of the codebase still references models/props/srcbox/srcbox.mdl (e.g., source_bridge.py:2051). This inconsistency would likely break cube spawning in some places.

Unfortunately to these problems I see, I have to close this. You could try send another one to fix or justify reasons for it though! Thank you for pull request tho!