Revert "refer to subsecton index in main index"

This reverts commit 6e62bd8.

Author: RDaxini

docs/sphinx/source/user_guide/index.rst

@@ -10,16 +10,25 @@ This user guide is an overview and explains some of the key features of pvlib.
    :caption: Getting started
    :maxdepth: 2
 
-   getting_started/index
+   getting_started/package_overview
+   getting_started/installation
+   getting_started/introtutorial
 
 .. toctree::
    :maxdepth: 2
    :caption: Modeling topics
 
-    modeling_topics/index
+   modeling_topics/pvsystem
+   modeling_topics/modelchain
+   modeling_topics/timetimezones
+   modeling_topics/bifacial
+   modeling_topics/clearsky
+   modeling_topics/weather_data
+   modeling_topics/singlediode
 
 .. toctree::
    :maxdepth: 2
    :caption: Extras
 
-   extras/index
+   extras/nomenclature
+   extras/faq