Provide custom information for the video reviewer field

[drnlm]

It would be useful to add some additional information around the video reviewer field, so the talk author is at least aware of the conference expectations - things like how long after the conference the review requests are likely to be, desired deadlines for review, that sort of thing.

Since this will vary depending on the conference, this needs to be customisable.

Probably the simplest option is to have a setting that will be inserted as a descriptive block in the appropriate form if it's present - maybe a markdown block?