Steam is distributed as a `.deb` file, for now only as an i686 package (the amd64 package only has documentation). When unpacked, it has a script called `steam` that in Ubuntu (their target distro) would go to `/usr/bin`. When run for the first time, this script copies some files to the user's home, which include another script that is the ultimate responsible for launching the steam binary, which is also in `$HOME`.
The current approach to deploy Steam in NixOS is composing a FHS-compatible chroot environment, as documented [here](https://sandervanderburg.blogspot.com/2013/09/composing-fhs-compatible-chroot.html). This allows us to have binaries in the expected paths without disrupting the system, and to avoid patching them to work in a non FHS environment.
Use `programs.steam.enable = true;` if you want to add steam to `systemPackages` and also enable a few workarounds as well as Steam controller support or other Steam supported controllers such as the DualShock 4 or Nintendo Switch Pro Controller.
The FHS-compatible chroot used for Steam can also be used to run other Linux games that expect a FHS environment. To use it, install the `steam-run` package and run the game with: