[docs] Fix misspelling of "settings". NFC (#22236)

"settings" was misspelled as "serttings" in the reference section of the
`docs` page. Fixed #22234.

URL: [../docs/index](https://emscripten.org/docs/index.html)

Author: adrian-javid

site/source/docs/index.rst

@@ -30,7 +30,7 @@ This comprehensive documentation set contains everything you need to know to use
 **Reference:**
 
 - :ref:`api-reference-index` is a reference for the Emscripten toolchain.
-- :ref:`settings-reference` is a reference of all the Emscripten compiler serttings.
+- :ref:`settings-reference` is a reference of all the Emscripten compiler settings.
 - :ref:`tools-reference` is a reference for the Emscripten integration APIs.
 - :ref:`Sanitizers` shows how to debug with sanitizers.
 - :ref:`Module-Splitting` is a guide to splitting modules and deferring the