docs: point users towards passing in self to buildClan

templates/clan/minimal-flake-parts/clan.nix

@@ -1,10 +1,11 @@
-{ inputs, ... }:
+{ self, inputs, ... }:
 {
   imports = [
     inputs.clan.flakeModules.default
   ];
   clan = {
     meta.name = "__CHANGE_ME__";
+    inherit self;
     specialArgs = {
       inherit inputs;
     };