Set up new sac project

I need to maintain the docker-compose environment as I should update the
hosting environment and we wanna deploy the docker image.

The ecosystem is using docker, I use podman.
I therefore need to configure docker hub as look up registry for podman
for unqualified images.

There doesn't seem to be a `toTOML` nixpkgs method. That's why I write
the contents of the file myself.

home/files/containers/registries.conf

@@ -0,0 +1 @@
+unqualified-search-registries = ["docker.io"]

home/xdg.nix

@@ -30,6 +30,8 @@
     "composer/update-channel".text = "stable";
     "composer/auth.json".source = ./files/composer/auth.json;
 
+    "containers/registries.conf".source = ./files/containers/registries.conf;
+
     # Handbrake
     "ghb/preferences.json".source = ./files/ghb/preferences.json;
     "ghb/presets.json".source = ./files/ghb/presets.json;