Add Adam Cox advice on Supervisor and Cron

[ekansa]

brief description of changes

@mradamcox pointed out a potential cron issue with starting supervisor

issues addressed

further comments

Hopefully this helps make supervisor/celery (which has been a vexing pain) more maintainable.

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This box must be checked

• [x] the PR branch was originally made from the base branch

This box should be checked

• [x] after these changes the docs build locally without error

This box should only be checked you intend to follow through on it (we can do it on our end too)

• [x] I will cherry-pick all commits in this PR into other branches that should have them after this PR is merged