Add a readthedocs build status badge
:target: https://travis-ci.org/PyCQA/bandit/
:alt: Build Status
+.. image:: https://readthedocs.org/projects/bandit/badge/?version=latest
+ :target: https://readthedocs.org/projects/bandit/
+ :alt: Docs Status
+
.. image:: https://img.shields.io/pypi/v/bandit.svg
:target: https://pypi.org/project/bandit/
:alt: Latest Version
