Docs: explain inventory imports

lib/inventory/build-inventory/interface.nix

@@ -20,6 +20,32 @@ let
   };
 
   importsOption = lib.mkOption {
+    description = ''
+      List of imported '.nix' files.
+
+          Each filename must be a string and is interpreted relative to the 'directory' passed to buildClan.
+          The import only happens if the machine is part of the service or role.
+
+          ## Example
+
+          To import the `special.nix` file
+
+          ```
+          . Clan Directory
+          ├── flake.nix
+          ...
+          └── modules
+              ├── special.nix
+              └── ...
+          ```
+
+          ```nix
+          {
+            imports = [ "modules/special.nix" ];
+          }
+          ```
+
+    '';
     default = [ ];
     type = types.listOf types.str;
   };