images/attic: init (#95)

Crate image with attic-client.

images/attic/default.nix

@@ -0,0 +1,10 @@
+{ docker-nixpkgs
+, attic-client
+}:
+(docker-nixpkgs.nix.override {
+  extraContents = [ attic-client ];
+}).overrideAttrs (prev: {
+  meta = (prev.meta or { }) // {
+    description = "Nix and Attic client image";
+  };
+})