docs: project config option: cache_dir

docs/strictdoc_01_user_guide.sdoc

@@ -2517,6 +2517,23 @@ The ``html_assets_strictdoc_dir`` allows changing the assets folder name:
     html_assets_strictdoc_dir = "assets"
 <<<
 
+[SECTION]
+TITLE: Path to cache dir
+
+[TEXT]
+STATEMENT: >>>
+StrictDoc uses caching when reading and writing artifacts. By default, all caches are written to the system's temporary directory (``$TMPDIR``).
+
+The ``cache_dir`` option in the configuration file allows specifying a custom directory, such as ``./output/build``. This setting can help make caching artifacts visible alongside documentation artifacts.
+
+.. code:: toml
+
+    [project]
+    cache_dir = "./output/cache"
+<<<
+
+[/SECTION]
+
 [/SECTION]
 
 [SECTION]