Add DISCOVER cookbook checklist

[Dr-G]

Add the (downloadable/printable) checklist to the Cookbook

[Dr-G]

https://docs.google.com/document/d/1aYx2WkR6GP0Ycdx6TVTAwKgCQ5UPf25odhKpuPsAa1o/edit#heading=h.2uvka8cnaqfv

[aterrel]

Here is a copy of the checklist that @Dr-G refers to: DISCOVER cookbook checklist for conference organisers.pdf