Fix doc: Jupyterfs has to be JupyterFs in config files

[jeflem]

Somewhere between 0.3.1 and 0.4.0 the former class Jupyterfs in config.py became JupyterFs. This change is not reflected in the docs (README.md). For instance, server-side resources config now has to be

c.JupyterFs.resources = [
    {
        "name": "local_test",
        "url": "osfs:///Users/foo/test"
    },
]

Note the capital F in c.JupyterFs.resources.