S3 Setup doc

[Viveckh]

What is this doing?

What kind of change does this PR introduce? (check at least one)

• [ ] Bugfix
• [ ] Feature
• [ ] Code style update
• [ ] Refactor
• [ ] Build-related changes
• [x] Other, please describe: documentation update

Does this PR introduce a breaking change? (check one)

• [ ] Yes
• [x] No

If yes, please describe how it impacts the application:

The PR fulfills these requirements:

• [x] It's submitted to the develop branch, not the master branch
• [x] When resolving a specific issue, it's referenced in the PR's title (e.g. Fix #xxx[,#xxx], where "xxx" is the issue number)
• [ ] New/updated tests are included

Other information: