wrappers: add meta.wrappers options to wrappers

Allows the docs to be a little less hard-coded.

Lays the groundwork for splitting up the platform-specific option docs
on a per-page basis.

wrappers/modules/nixos.nix

@@ -5,4 +5,8 @@
   };
 
   imports = [ ./shared.nix ];
+
+  config = {
+    meta.wrapper.name = "NixOS";
+  };
 }