* docs: Add README to lms/templates/oauth2_provider

We wanted to move this single template into a djangoapp,
but there are technical limitations to us doing so.
This README helps explain the limitations so
future generations will know why this is here.

* Update lms/templates/oauth2_provider/README.rst

Co-authored-by: Robert Raposa <rraposa@edx.org>

* Update lms/templates/oauth2_provider/README.rst

Co-authored-by: Robert Raposa <rraposa@edx.org>

Co-authored-by: Robert Raposa <rraposa@edx.org>