Missing documentation for c.Exchange.root and c.Exchange.path_includes_course

[lahwaacz]

The documentation for Exchanging assignment files has an example containing

c.Exchange.root = "/tmp/exchange"

And Using nbgrader with JupyterHub has an example containing

c.Exchange.path_includes_course = True

However, none of these two settings is described in the documentation off Configuration options and they also don't show up in the output of nbgrader --help-all. I'm wondering what are the default values and how these two options play together, but it seems impossible to find.

[shreve]

Related to and likely solved by #1761