docs(backend_layout_and_approach): link django app patterns

source/developers/concepts/backend_layout_and_approach.rst

@@ -1,7 +1,7 @@
 Backend Layout and Approach
 ###########################
 
-`OEP-49 <https://open-edx-proposals.readthedocs.io/en/latest/architectural-decisions/oep-0049-django-app-patterns.html>`_ defines the common conventions used for Django apps written for this project.
+`OEP-49 <https://open-edx-proposals.readthedocs.io/en/latest/best-practices/oep-0049-django-app-patterns.html>`_ defines the common conventions used for Django apps written for this project.
 
 New apps, services, and libraries should be created using `edx-cookiecutters <https://github.com/openedx/edx-cookiecutters>`_, which will fill in a lot of the boilerplate pieces for you (e.g. license, translations, testing dependencies).