move options to separate modules, set up mkDocs generation

modules/flake-parts.nix

@@ -1,9 +1,5 @@
-{ inputs, self, ...}: {
+{ inputs, self, ... }: {
   systems = [
     "x86_64-linux"
   ];
-
-  flake.flakeModules = {
-    docs-entry-point = inputs.import-tree "${self}/modules";
-  };
-}
+}