add link to auto_mode in sphinx-autodoc2

fixes executablebooks#1031

Author: nerdoc

docs/syntax/code_and_apis.md

@@ -170,7 +170,7 @@ Sphinx and MyST provide means to analyse source code and automatically generate
 
 As opposed to `sphinx.ext.autodoc`, `sphinx-autodoc2` performs static (rather than dynamic) analysis of the source code, integrates full package documenting, and also allows for docstrings to be written in both RestructureText and MyST.
 
-The `auto_mode` will automatically generate the full API documentation, as shown <project:/apidocs/index.rst>.
+The [sphinx-autodoc2's `auto_mode` config variable](https://sphinx-autodoc2.readthedocs.io/en/latest/config.html#confval-autodoc2_packages-auto_mode) (which per default is `True`)  will automatically generate the full API documentation, as shown <project:/apidocs/index.rst>.
 
 Alternatively, the `autodoc2-object` directive can be used to generate documentation for a single object.
 To embed in a MyST document the MyST `render_plugin` should be specified, for example: