Update to install strings

[IAmALittleTeaPot]

Original instructions:
REMOTE_AUTH_BACKEND = 'utilities.auth_backends.RemoteUserBackend'

Netbox 4:
REMOTE_AUTH_BACKEND = 'netbox.authentication.RemoteUserBackend'

[IAmALittleTeaPot]

To be more clear, maybe remove the ## in the install instructions for the newer versions and put notes in for the older versions