change subsection title -> modeling topcis

Co-Authored-By: Kevin Anderson <[email protected]>

Author: RDaxini

docs/sphinx/source/user_guide/index.rst

@@ -15,7 +15,7 @@ This user guide is an overview and explains some of the key features of pvlib.
    introtutorial
 
 .. toctree::
-   :caption: Advanced usage
+   :caption: Modeling topics
    :maxdepth: 2
 
    pvsystem