User documentation - WIP

[patriciabt]

Description of the Change

I added the first iteration of the user documentation, with media files. Steve Mosby @malgrauk is going to work on better texts.

Changelog Entry

Added - User documentation

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.

[what-the-diff]

PR Summary

• Enhanced Documentation
  Significant updates have been made to the documentation for better user-guidance. Specifically, this includes new images and markdown files, demonstrating the installation process, understanding the GatherPress Alpha, adapting GatherPress settings, steps to create or edit venues and events, and outlining GatherPress topics. This improvement aims to make corresponding product features more understandable and intuitive for our users.

[patriciabt]

@mauteri said OK to merge as it's only new files and text/media (no code)