add comment on updating Airtable rev-prod for new editors

[mpadge]

@maelle The change to https://github.com/ropensci/dev_guide/blob/main/scripts/airtable-get-data.R is key - some editor values are NA, and these are retained and listed as editors at https://devguide.ropensci.org/softwarereview_intro.html#editorial-team. The Airtable fields are empty, just like the standard NULL ones, so I don't know where the NAs come from, but this fixes. I've also updated all Airtable records, and added extra lines to instructions on what I did there. This should fix the list.

(Oh, and we currently have only one ed on leave, Anna Krystalli, and she's cool with being unlisted there; there'll likely be another soon joining the indefinite-leave crew, but treating them as Emeritus in this context is fine.)

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Checklist for dev guide maintainers, do not delete 😸

• Review of the content in the initial language.
• News item.
• Translation of the content in other languages.
• Review of the translations.

[maelle]

thank you!!