Add docs on markdown usage (#50)

docs/source/advanced-configuration.rst

@@ -292,6 +292,11 @@ Your URI template can use the following variables:
 - ``{suffix}`` - The source file suffix (e.g., ``.rst``, ``.md``) - may be empty if no source file exists
 - ``{sourcelink_suffix}`` - The suffix from ``html_sourcelink_suffix`` configuration (e.g., ``.txt``)
 
+.. tip::
+   Instead of using the default of linking to ``_sources``, you can generate Markdown files from your documentation and link to those in ``llms.txt``.
+   See this package's `CMake setup <https://github.com/jdillard/sphinx-llms-txt>`_ for an example of building both HTML and Markdown in parallel.
+   Note that ``_sources`` is still needed for ``llms-full.txt`` at this time.
+
 .. _integration_examples:
 
 Integration Examples