Potentially improve the docs for file upload

[Martinsos]

We had a user struggle a bit with getting the file-upload to work: https://discord.com/channels/686873244791210014/1243395173006966834/1243395173006966834 .

Seems like there is some capacity to improve our docs to potentially help avoid this in the future:

Hey! The docs are very helpful, but this situation, which I imagine impacts more than just me, was because of some gaps where things weren’t 1:1 with the documentation. I created a new aws root account. Then an iam account. The problem had to do with permissions. From the root user, you can give an IAM user full S3 permissions, OR full IAM permissions. In order to create a bucket I needed to give it S3 access, and I had to toggle it to IAM access when creating access keys. AWS shows red when trying to access something you lack permissions for, and that’s what clued me in on what specific permission rules I needed to create and add individually.
After adjusting permissions for awhile I got it to work, but none of that aligned with how straightforward the docs made it look.