Document --auth-group for kachery-daemon

[magland]

An excerpt from an email to franklab:

Kachery daemon authorization system has been updated to allow connecting to a single daemon from multiple machines. Here's what you need to do:

When starting the daemon, use --auth-group <group-name>. Then any user in that group will have access to the daemon, as long as they have the following two environment variables set:

KACHERY_DAEMON_PORT=
KACHERY_DAEMON_HOST=
KACHERY_TEMP_DIR=

Note that KACHERY_TEMP_DIR is different from KACHERY_STORAGE_DIR

Note also that the kachery storage dir must be in a shared location that is at the same absolute path on all of the involved machines.