getSessions() is missing

[WhyINeedToFillUsername]

Describe the bug
According to the readme at https://github.com/solid/solid-auth-fetcher/blob/master/README.md#logging-in-multiple-users, there should be getSessions() method. However, after using the library from npm, there is no exported member, nor implementation of the getSessions() method.

To Reproduce
Steps to reproduce the behavior:

1. npm install solid-auth-fetcher
2. import { getSessions } from 'solid-auth-fetcher'
3. no exported member getSessions

Expected behavior
getSessions implemented as promoted :)

Additional context
latest build - 1.3.5

[josephguillaume]

The core functionality for multiple users in this example is uniqueLogin, which itself is just a wrapper around loginHelper that doesn't specify a localUserId. getSessions is just used to check if the webid is already logged in (but looks like there's a typo in the example anyway).
If I understand correctly, storage is always by localUserId, so there is currently no storage that getSessions could iterate through sessions created by uniqueLogin.
Unless I've misunderstood something, I therefore suggest simply deleting this part of the README.md.

This issue could be left open as a getSessions function could still be written that iterates through data stored for different localUserIds, but it wouldn't be used with uniqueLogin specifically.
A localUserId could also also be generated when missing, perhaps in setForUser, but this requires more thought.