docs: self host documentation with mkDocs

docs/flake-module.nix

@@ -0,0 +1,13 @@
+{ inputs, ... }:
+{
+  perSystem =
+    { self', pkgs, ... }:
+    {
+      devShells.docs = pkgs.callPackage ./shell.nix { inherit (self'.packages) docs; };
+      packages = {
+        docs = pkgs.python3.pkgs.callPackage ./default.nix { inherit (inputs) nixpkgs; };
+      };
+
+      checks = self'.packages.clan-cli.tests;
+    };
+}