Update quart_extensions.rst

Added Quart-SqlAlchemy which I found look for the solution that this provided. I added it to the Quart Extensions list, so that it can be found by other people when they are getting started with Quart. This extension has multiple contributors and seems to be actively developed.

Author: crood58

docs/how_to_guides/quart_extensions.rst

@@ -42,6 +42,7 @@ here,
   <https://github.com/enchant97/quart-redis>`_ Redis connection handling
 - `Webargs-Quart <https://github.com/esfoobar/webargs-quart>`_ Webargs
   parsing for Quart.
+- `Quart-SqlAlchemy <https://github.com/joeblackwaslike/quart-sqlalchemy>`_ Quart-SQLAlchemy provides a simple wrapper for SQLAlchemy.
 - `Quart-WTF <https://github.com/Quart-Addons/quart-wtf>`_ Simple integration of Quart
   and WTForms. Including CSRF and file uploading.
 - `Quart-Schema <https://github.com/pgjones/quart-schema>`_ Schema