Docs: update the installation note (#1595)

* Docs: update the installation note

Translated string work with/without the theme added into the ``extensions``.
However, it's still required to be inside the extensions because of
``sphinxcontrib-jquery``.

I'm keeping the note, but changing it content.

* Update docs/installing.rst

Co-authored-by: Anthony <[email protected]>

---------

Co-authored-by: Anthony <[email protected]>

Author: humitos

docs/installing.rst

@@ -31,15 +31,13 @@ In your Sphinx project's ``conf.py`` file, add ``sphinx_rtd_theme`` to the list
 
 .. note::
 
-   Adding this theme as an extension is what enables localization of theme
-   strings in your translated output. If these strings are not translated in
-   your output, either we lack the localized strings for your locale, or you
-   are using an old version of the theme.
-
-   ..
-      comment about this note: it's possibly not necessary to add the theme as an extension.
-      Rather, this is an issue caused by setting html_theme_path.
-      See: https://github.com/readthedocs/readthedocs.org/pull/9654
+   Adding this theme as an extension activates the ``sphinxcontrib-jquery`` extension,
+   which is required for search, smooth scrolling, and the flyout menu.
+   If any of these features don't work, make sure you have the theme declared in your ``extensions``.
+
+   .. More context for this note:
+        * https://github.com/readthedocs/sphinx_rtd_theme/issues/1434#issuecomment-2288359582
+        * https://github.com/readthedocs/sphinx_rtd_theme/issues/1222#issuecomment-2296703160
 
 
 .. _howto_upgrade: