fix(docs): tighten up validation for meta.name and improved description

lib/inventory/build-inventory/meta-interface.nix

@@ -4,11 +4,14 @@ let
 
   metaOptions = {
     name = lib.mkOption {
-      type = types.str;
+      type = types.strMatching "[a-zA-Z0-9_-]*";
+      example = "my_clan";
       description = ''
         Name of the clan.
 
         Needs to be (globally) unique, as this determines the folder name where the flake gets downloaded to.
+
+        Should only contain alphanumeric characters, `_` and `-`.
       '';
     };
     description = lib.mkOption {