TODO: For now, the invite flow implies that the user has to explicitly
accept by adding one or more clients via external commit as part of the "Join"
flow. In the future, we can either make the "Invite" flow more versatile and
allow for Welcome based invitations, or create an additional "Add" flow, that
allows participants to add other users (and their clients) directly via
Welcome.
That TODO is a bit outdated (meaning I forgot to remove it as part of the PR that added the Add flow). We now have an "Add" section in the document, so I think we can close this.