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/shared.nix

@@ -2,5 +2,13 @@
 {
   options = {
     enable = lib.mkEnableOption "nixvim";
+
+    meta.wrapper = {
+      name = lib.mkOption {
+        type = lib.types.str;
+        description = "The human-readable name of this nixvim wrapper. Used in documentation.";
+        internal = true;
+      };
+    };
   };
 }