Update roles/members/sub-team info

[linsun]

[ ] Document how role, function-based members, or sub-teams are assigned, onboarded, and removed for specific teams (example: Security Response Committee).

While reviewing the governance doc, I don't see how team are assigned or onboarded, or removed.

cc @SantiagoTorres

[trishankatdatadog]

Same like here, do you need documentation about how individuals are onboarded to the org as well as teams?