prepare metadata needs some information on how to actual create metadata

This is mostly about how to interact with the metadata service. (And all very good/important).
But then there's only the littlest bit about writing metadata in the instrument section. I think we maybe want this on a more generic level and higher up (or perhaps as a separate page).

Additional notes:
- no information about aquisition or processing or qc. And I think this is intentional because I think the intention for the scope of the page is not about preparing metadata writ large, but having metadata ready before acquisition. So I think there should be another page about metadata a bit more generally, and then this should be a subpage of that? Not sure.
- the heading structure is confusing on this page.