Document how to ensure you're using TLSv1.1 or, preferably, TLSv1.2 on Windows, macOS, and non-macOS Unix.

For example, the system Pythons on macOS before 10.3 only support TLSv1.0, so installing Python from python.org, homebrew, etc. is required.

Add this documentation to the following pages:
https://api.mongodb.com/python/current/atlas.html
https://api.mongodb.com/python/current/examples/tls.html