[Halla_parity] update of HOWTO page

[Robert Michaels]

To all experts on subsystems:   Please remember to update the
relevant section of the HOWTO page for running PVDIS.  I realize
everyone is busy with hardware and tests, but the page must be
considered an essential part of the job and should be done ASAP.
If you're an expert you know what page I'm talking about.
All our files owned by Unix group a-parity with group-write
permission.  This allows everyone to correct everyone else's
mistakes -- a style we've always found useful.  If you correct
someone's mistake, tell them by e-mail.

thanks
Bob