Mention that -fakestat fakes local cellular mounts

Mention that -fakestat fakes local cellular mounts

The afsd man page says that -fakestat only fakes stat information for
cross-cell mount points. Technically it fakes stat information for all
cellular mount points, local or foreign. Most people shouldn't care,
but note the difference, since some places do have local cellular
mount points.

Change-Id: I9bc61a0284b7d04439578a4fc5a6adf791217463
Reviewed-on: http://gerrit.openafs.org/1979
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Russ Allbery <rra@stanford.edu>
Tested-by: Russ Allbery <rra@stanford.edu>