Document Grist integrations

[marksteward]

We have various processes that want to use up-to-date website data, but people want to use some sort of open-ended editing system. For example:

• Signage for installations
• Arcade listing
• Documentation for exhibitors to put in their portfolio

For these and any more Grists, we should check that they're importing the data appropriately (i.e. to a clean sheet that can be reimported), and consider whether they should be brought into the main site, like the arcade pages.

For this ticket, let's document how to set up a Grist that works properly, and any existing known integrations.

[marksteward]

Arcade had a manual "CFP" https://grist.orga.emfcamp.org/dfSdHXyzPRGv/Arcade/p/6

[SamLR]

Similar integrations/flows into freescount should also be documented