Add a 'For Enterprise' section to the README

README.rst

 .. image:: https://tidelift.com/badges/package/pypi/PROJECT
    :target: https://tidelift.com/subscription/pkg/pypi-PROJECT?utm_source=pypi-PROJECT&utm_medium=readme
 
+For Enterprise
+==============
+
+Available as part of the Tidelift Subscription.
+
+This project and the maintainers of thousands of other packages are working with Tidelift to deliver one enterprise subscription that covers all of the open source you use.
+
+`Learn more <https://tidelift.com/subscription/pkg/pypi-PROJECT?utm_source=pypi-PROJECT&utm_medium=referral&utm_campaign=github>`_.
+
 Security Contact
 ================