Add section about Template naming and locations to PAGEVIEW (#1546)

* Update Index.rst

I just try to get PAGEVIEW running and get errors like:

Tried resolving a template file for controller action "Default->Pages/Default" in format ".html", but none of the paths contained the expected template file (Default/Pages/Default.html).

That's why I would prefer to provide a running example in first section, before we start explaining the containing variables for Fluid templating.

* Apply suggestions from code review

Co-authored-by: Garvin Hicking <38074677+fe-hicking@users.noreply.github.com>

* Improve content

* Update Documentation/ContentObjects/Pageview/Index.rst

* Update Documentation/ContentObjects/Pageview/Index.rst

---------

Co-authored-by: Lina Wolf <48202465+linawolf@users.noreply.github.com>
Co-authored-by: Garvin Hicking <38074677+fe-hicking@users.noreply.github.com>

Author: 3 people

Documentation/ContentObjects/Pageview/Index.rst

@@ -40,6 +40,42 @@ Example: Display a page with Fluid templates
     :language: typoscript
     :caption: EXT:my_sitepackage/Configuration/TypoScript/setup.typoscript
 
+..  _cobj-pageview-template-naming:
+
+Template naming and locations
+=============================
+
+To ensure proper rendering, the following requirements and
+fallback mechanisms apply:
+
+..  _cobj-pageview-template-naming-path:
+
+Target path structure
+---------------------
+
+*   The target directory **must contain a folder named :directory:`Pages/`**.
+*   This folder must contain Fluid templates in :file`*.html` format.
+
+..  _cobj-pageview-template-naming-conventions:
+
+Template naming convention
+--------------------------
+
+*   The Fluid template file **must** match the name of the selected backend layout
+    of your current page.
+*   The first letter of the Fluid template file must be **uppercase**.
+
+..  _cobj-pageview-template-naming-fallback:
+
+Fallback behavior when no backend layout is defined
+----------------------------------------------------
+
+*   If the page record does not specify a backend layout, TYPO3 tries to detect
+    next-level backend layouts by traversing up the page rootline.
+*   If still no backend layout could be found, TYPO3 falls back to `Default.html`.
+*   If you explicitly set the backend layout to `none`, a Fluid template
+    with name :file:`None.html` will be used.
+
 .. _cobj-pageview-data:
 
 Default variables in Fluid templates