1. Give them this link: <https://groups.google.com/forum/m/#!forum/sfbay-dfir>
2. There is an "Apply for membership" link there.  They should click it.
3. When applying, they need to:
 a. Use their work account as proof.
 b. Include a message to the manager with:
   1. Who they are
   2. Who they know in the group
   3. Where they work
   4. What they do there
 c. Click Apply to join this group

The admins will get a notice and approve (or not).