Rearrange user guide files into subfolders (#2411)

* subfolders according to current subsections

* index.rst file additions/modifications

* edit maxdepth

* userguide/index

* Update index.rst

* recover original rendering format

* change max depth

* Update index.rst

* refer to subsecton index in main index

* remove extra spaces

* try hidden?

* Revert "try hidden?"

This reverts commit 3dc9819.

* Revert "remove extra spaces"

This reverts commit d57c391.

* Revert "refer to subsecton index in main index"

This reverts commit 6e62bd8.

* remove spaces

* match subsection order

* more extra spaces

* Revert "more extra spaces"

This reverts commit 9764b08.

* remove sublevel index.rst

Author: RDaxini

docs/sphinx/source/user_guide/faq.rst renamed to docs/sphinx/source/user_guide/extras/faq.rst

@@ -133,7 +133,7 @@ Follow these steps to obtain the library using git/GitHub:
    This button is circled in the image below. Remember the system path that
    you clone the library to.
 
-.. image:: ../_images/clonebutton.png
+.. image:: ../../_images/clonebutton.png
 
 Please see GitHub's
 `Forking Projects <https://guides.github.com/activities/forking/>`_,

docs/sphinx/source/user_guide/nomenclature.rst renamed to docs/sphinx/source/user_guide/extras/nomenclature.rst

@@ -9,26 +9,26 @@ This user guide is an overview and explains some of the key features of pvlib.
 .. toctree::
    :caption: Getting started
    :maxdepth: 2
-   
-   package_overview
-   installation
-   introtutorial
-   
+
+   getting_started/package_overview
+   getting_started/installation
+   getting_started/introtutorial
+
 .. toctree::
-   :caption: Modeling topics
    :maxdepth: 2
-   
-   pvsystem
-   modelchain
-   timetimezones
-   bifacial
-   clearsky
-   weather_data
-   singlediode
+   :caption: Modeling topics
+
+   modeling_topics/pvsystem
+   modeling_topics/modelchain
+   modeling_topics/timetimezones
+   modeling_topics/bifacial
+   modeling_topics/clearsky
+   modeling_topics/weather_data
+   modeling_topics/singlediode
 
 .. toctree::
-   :caption: Extras
    :maxdepth: 2
+   :caption: Extras
 
-   nomenclature
-   faq
+   extras/nomenclature
+   extras/faq