add PMM team onboarding doc
Why is this change being made?
Updating the handbook to include the PMM team onboarding doc
Issue for reference: https://gitlab.com/gitlab-com/marketing/product-marketing/issues/1767
Edited by Parker Ennis (he/him)
Updating the handbook to include the PMM team onboarding doc
Issue for reference: https://gitlab.com/gitlab-com/marketing/product-marketing/issues/1767