Demonstrate how publishing workflows differ for admins and contributors

## The problem to solve

Documenting [a discussion in Discord](https://discord.com/channels/517772094482677790/701815369005924374/964278504457912360): I was not aware that the publishing workflow looked different for admins (draft --> published) and contributors (draft --> submitted for review). Providing a short demo, e.g. on the [Users doc page](https://v3.docs.apostrophecms.org/guide/users.html), could highlight this, which may be an important feature for users (it was for me!).

## Proposed solution

On the [Users doc page](https://v3.docs.apostrophecms.org/guide/users.html), provide the following demo (with screenshots as appropriate)

1. Log on as admin (already created during setup)
2. Create new content, publish it. Call out the buttons that were clicked and how draft went to published
3. Create a new user that has contributor permissions (following instructions higher up on the page)
4. Log in as the new user
5. Modify the content created in step 2, submit it. Call out the different workflow.
6. Log back in as the admin, show how the submitted draft appears in the inbox, and how to publish the proposed changes.

## Alternatives

The demo isn't strictly necessary, e.g. this could just be described. Seeing how the UI changes might be valuable though.

## Additional context

N/A