[STEAM] Added docs and some tweaks for Linux Steam, also added a new env var for it #7026

Job	Run time
build (X64, Release, ubuntu-latest)	3m 20s
build (RISCV, Trace, ubuntu-latest)	20m 47s
build (RK3588, Trace, ubuntu-22.04-arm)	4m 49s
build (RISCV, StaticBuild, ubuntu-latest)	17m 47s
build (RISCV, Box32, ubuntu-latest)	21m 11s
build (X64, Trace, ubuntu-latest)	3m 7s
build (X64, Box32, ubuntu-latest)	2m 58s
build (RK3588, StaticBuild, ubuntu-22.04-arm)	2m 48s
build (RISCV, Release, ubuntu-latest)	20m 40s
build (RK3588, Box32, ubuntu-22.04-arm)	4m 0s
build (ARM64, StaticBuild, ubuntu-22.04-arm)	2m 33s
build (RK3588, Release, ubuntu-22.04-arm)	4m 9s
build (ARM64, Box32, ubuntu-22.04-arm)	3m 44s
build (ARM64, Release, ubuntu-22.04-arm)	3m 54s
build (ANDROID, Release, ubuntu-latest)	5m 11s
build (ARM64, Trace, ubuntu-22.04-arm)	4m 24s
build (ANDROID_GLIBC, Trace, ubuntu-22.04-arm)	4m 47s
build (ANDROID_GLIBC, Box32, ubuntu-22.04-arm)	4m 4s
build (WOW64, Release, ubuntu-22.04-arm)	4m 5s
build (ARM64-GCC-8, Box32, ubuntu-22.04-arm)	4m 7s
build (ARM64-GCC-8, Release, ubuntu-22.04-arm)	4m 15s
build (LARCH64, StaticBuild, ubuntu-latest)	5m 42s
build (TERMUX, Release, ubuntu-latest)	3m 14s
build (ANDROID_GLIBC, StaticBuild, ubuntu-22.04-arm)	2m 43s
build (ANDROID_GLIBC, Release, ubuntu-22.04-arm)	4m 33s
build (LARCH64, Release, ubuntu-latest)	7m 1s
build (LARCH64, Box32, ubuntu-latest)	6m 52s
	2h 56m 45s

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