FeedbackXBlock README suggests unsupported Tutor config format

[regisb]

In the FeedbackXBlock readme, the recommended approach is to create a Tutor plugin as a YAML file. But plugins as YAML files are no longer the recommended approach to create Tutor plugins. Instead, plugin developers are encouraged to create either single-file Python modules or full-fledged Python packages: https://docs.tutor.edly.io/tutorials/plugin.html

[samuelallan72]

This yaml file method doesn't appear to be supported at all in the latest Tutor version.

[kdmccormick]

I transferred this over from https://github.com/openedx/FeedbackXBlock