Documentation: restore a controller from backup is a bit optimistic

[aieri]

Docs page: https://juju.is/docs/juju/manage-controllers

Docs source: https://discourse.charmhub.io/t/how-to-manage-controllers/1111

Issue:

The juju.is docs regarding restoring a backup aren't explicit about the current limitations of the juju-restore tool. While the tool's specific github docs do offer a disclaimer about what to expect, these may be missed by a user that is only browsing juju.is.