home: jujutsu: explicitly create 'conf.d'

This is to serve as a reminder of _how_ to add a local configuration
file.

modules/home/delta/default.nix

@@ -86,10 +86,8 @@ in
         };
 
         ui = {
-          diff = {
-            # Delta expects a `git diff` input
-            format = "git";
-          };
+          # Delta expects a `git diff` input
+          diff-formatter = ":git";
 
           pager = "${lib.getExe cfg.package}";
         };