In README.rst add build status badge for github actions CI
This replaces the one for travis-ci which is no longer used.
:target: https://pypi.org/project/django-storages/
:alt: PyPI Version
-.. image:: https://travis-ci.org/jschneier/django-storages.svg?branch=master
- :target: https://travis-ci.org/jschneier/django-storages
+.. image:: https://github.com/jschneier/django-storages/actions/workflows/ci.yml/badge.svg
+ :target: https://github.com/jschneier/django-storages/actions/workflows/ci.yml
:alt: Build Status
Installation
