Add a delay to minutes sending

[rhiaro]

Github pages can take up to 5 minutes to build, so often the link to generated minutes is sent out by email and twitter before the page is ready. Maybe we can add a delay in the github actions script to minimise chances of people clicking the link immediately and getting a 404.

Admittedly the only people likely to do that are the people generating the minutes, to check it worked, so not high priority.. but just in case..