steam: restore and document timezone hack

Fixes #379623 ?

pkgs/by-name/st/steam/package.nix

@@ -89,6 +89,15 @@ let
       export LIBVA_DRIVERS_PATH=/run/opengl-driver/lib/dri:/run/opengl-driver-32/lib/dri
       export VDPAU_DRIVER_PATH=/run/opengl-driver/lib/vdpau:/run/opengl-driver-32/lib/vdpau
 
+      # Steam gets confused by the symlinks to bind mounts to symlinks /etc/localtime ends up being, so help it out.
+      # See also: https://github.com/flathub/com.valvesoftware.Steam/blob/28481f09f33c12b6ac7421d13af9ed1523c54ec4/steam_wrapper/steam_wrapper.py#L160
+      if [ -z ''${TZ+x} ]; then
+        new_TZ="$(readlink -f /etc/localtime | grep -P -o '(?<=/zoneinfo/).*$')"
+        if [ $? -eq 0 ]; then
+          export TZ="$new_TZ"
+        fi
+      fi
+
       set -a
       ${lib.toShellVars extraEnv}
       set +a