docs: self host documentation with mkDocs

docs/default.nix

@@ -0,0 +1,26 @@
+{ pkgs, ... }:
+pkgs.stdenv.mkDerivation {
+  name = "clan-documentation";
+
+  src = ./.;
+
+  nativeBuildInputs =
+    [ pkgs.python3 ]
+    ++ (with pkgs.python3Packages; [
+      mkdocs
+      mkdocs-material
+      mkdocs-drawio-exporter
+      mkdocs-swagger-ui-tag
+      plantuml-markdown
+    ]);
+
+  buildPhase = ''
+    mkdocs build --strict
+
+    ls -la .
+  '';
+
+  installPhase = ''
+    cp -a site/ $out/
+  '';
+}