Added steps for umu & proton-cachyos for faugus launcher

[SlowNicoFish]

Added steps according to Faugus/faugus-launcher#41

[1Naim]

+ @loathingKernel

[loathingKernel]

This is outdated at this point, and the UMU_NO_RUNTIME=1 is not possible to do in upstream umu-launcher, it is a custom patch only CachyOS carries presently. I am trying to upstream it.

In any case, faugus, the application, is wrong about this. umu-launcher can launch without the need to symlink just by providing the absolute path to /usr/share/steam/compatibilitytools.d/proton-cachyos. For CachyOS, UMU_NO_RUNTIME=1 is applicable and still required. What I do not know is if faugus has added some automatic detection to infer the use of that env variable.