Add guidance around setting up a submission in the submission portal first

[pkalita-lbl]

Until we implement features like setting up contributors and roles in the app (#197) or duplicating samples (#175), some people may find it beneficial to start their submission in the submission portal before going into the field. We should add some guidance about that to the Guide tab.

[pkalita-lbl]

Notes from 2024-11-18 squad meeting:

• Also consider talking about going to the Submission Portal after finishing field work to finalize the study/sample metadata and submit it to us. "Finalizing" the submission.
• Eric floated the idea that this is similar to "staging" changes in Git (i.e. getting ready to commit them)
• Patrick suggested we add some kind of "How the app interacts with the Submission Portal" section to the Guide tab. Maybe this could/should be shown to the user the first time they use the app (using the in-app tours functionality?)