OK - I'll add this between export from oTree Studio and upload to oTree Hub.
My new DEMO_PAGE_INTRO_HTML text now appears here (right hand box, running into text "To add to this list, create a new session config." which could be separate):
However, it does not yet appear here (despite the source code and last updated link having updated):
https://www.otreehub.com/projects/mdt-intr-exp-met/
Not so important for my particular example, but I think there is value in making this field easier to set and encouraging people to use it - it could make the public projects listing far more informative.
Peter