steamPackages.chrootenv: add file command

Noticed that the setup.sh for steam was trying to call the file command.
I'm not sure what the ramifications are for these missing,
but some steam features are quietly disabled when they
don't follow happy paths.

pkgs/games/steam/chrootenv.nix

@@ -100,6 +100,9 @@ in buildFHSUserEnv rec {
 
     # friends options won't display "Launch Game" without it
     lsof
+
+    # called by steam's setup.sh
+    file
   ] ++ (if (!nativeOnly) then [
     (steamPackages.steam-runtime-wrapped.override {
       inherit runtimeOnly;