docs/home-manager: eval options without checking config definitions

By default `lib.evalModules` will check all config definitions match
a declared option (or a freeform type), leading to errors like:

    error: The option `wrapRc' does not exist.

Setting `_module.freeformType` or `_module.check` will disable this,
allowing us to evaluate the option declaration without checking the
config definitions.

wrappers/modules/hm.nix

@@ -13,4 +13,9 @@
   };
 
   imports = [ ./enable.nix ];
+
+  config = {
+    wrapRc = lib.mkOptionDefault false;
+    impureRtp = lib.mkOptionDefault true;
+  };
 }