Read the Docs builds are failing because of missing configuration file

[martey]

This means all versions of the documentation past 3.3 are not accessible. This seems to have started a year ago - see https://app.readthedocs.org/projects/invocations/builds/:

The failed builds have the same error message:

The required .readthedocs.yaml configuration file was not found at repository's root.
Learn how to use this file in our configuration file tutorial.

https://blog.readthedocs.com/migrate-configuration-v2/ contains more information about this change in Read the Docs's behavior. Please let me know if you would appreciate a pull request containing a configuration file to fix this problem and I can make one.