Add explanation of next steps on file upload page of Shiny App

[rootsandberries]

I think people might get hung up on this tab not knowing what to do next. Can we add some text below the box on the left? Something like:

Double click the rows to edit source names and fill in label fields. String fields are optional. For records that are associated with a screening phase, rather than a source, change the source name to NA. In the cite label field, enter 'search' for search results files and 'screened' or 'final' for different screening phases.

This might be a little simplistic, but I think this would help users know what to do here.