self-hosted: document the importance of GRIST_DEFAULT_EMAIL

[jordigh]

I need to reference this value from another PR

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[paulfitz]

An extra gotcha that often trips people up is ownership of the team site created on first run if GRIST_SINGLE_ORG is set
https://github.com/gristlabs/grist-core/blob/1f984ab5a7338430ab98cba42cb0d7b0daa229bc/stubs/app/server/server.ts#L63-L90
The owner will be GRIST_DEFAULT_EMAIL so things get very confusing if that email is changed but the team site is kept (and is now inaccessible!)

[jordigh]

I added a comment about this. Does that help?

[paulfitz]

Thanks Jordi! One more note.

[paulfitz]

This could be a little more precise.

If GRIST_SINGLE_ORG is set, then on start-up Grist will create the specified team site if isn't already present. When creating it, it will make the current administrator an owner of it. Before changing the administrator, it is a good idea to use team sharing options to add new owners to the team site, since apart from initial creation, administrators have no automatic right to team site membership.

[jordigh]

I added your note. Does that look better?

[paulfitz]

Thanks @jordigh