CI.md

This is a summary of the Python versions and platforms covered by the different CI platforms:

	3.6	3.7	3.8
Linux	Travis CI / CircleCI	AppVeyor¹ / GitHub Actions	Azure Pipelines
macOS	CircleCI	AppVeyor¹ / GitHub Actions	Azure Pipelines
Windows	Travis CI / Azure Pipelines	AppVeyor¹ / GitHub Actions	Azure Pipelines

¹ AppVeyor only runs the "basic" test to reduce load.

Non-x86 architectures are covered on Travis CI using Python 3.6.