docs: Allow to generate man pages for nixvim (#686)

man-docs/nixvim-render-docs/default.nix

@@ -0,0 +1,31 @@
+{
+  python3,
+  lib,
+  nixos-render-docs,
+}:
+python3.pkgs.buildPythonApplication {
+  pname = "nixvim-render-docs";
+  version = "0.0";
+  format = "pyproject";
+
+  src = lib.cleanSourceWith {
+    filter = name: type:
+      lib.cleanSourceFilter name type
+      && ! (type
+        == "directory"
+        && builtins.elem (baseNameOf name) [
+          ".pytest_cache"
+          ".mypy_cache"
+          "__pycache__"
+        ]);
+    src = ./src;
+  };
+
+  nativeBuildInputs = with python3.pkgs; [
+    setuptools
+  ];
+
+  propagatedBuildInputs = [
+    nixos-render-docs
+  ];
+}