docs: fix documentation generation

docs.nix

@@ -0,0 +1,35 @@
+{ pkgs, lib, modules, ... }:
+let
+  options = lib.evalModules {
+    modules = modules;
+    specialArgs = { inherit pkgs lib; };
+  };
+  docs = pkgs.nixosOptionsDoc {
+    # If we don't do this, we end up with _module.args on the generated options, which we do not want
+    options = lib.filterAttrs (k: _: k != "_module") options.options;
+    warningsAreErrors = false;
+  };
+  asciidoc = docs.optionsAsciiDoc;
+in
+pkgs.stdenv.mkDerivation {
+  name = "nixvim-docs";
+
+  src = asciidoc;
+  buildInputs = [
+    pkgs.asciidoctor
+  ];
+
+  phases = [ "buildPhase" ];
+
+  buildPhase = ''
+    mkdir -p $out/share
+    cat <<EOF > header.adoc
+    = NixVim options
+    This lists all the options available for NixVim.
+    :toc:
+
+    EOF
+    cat header.adoc $src > tmp.adoc
+    asciidoctor tmp.adoc -o $out/share/index.html
+  '';
+}