Looks like we won't have file uploads, at least initially.
The common file upload system extension is kind of garbage, isn't maintained, and does not work.
Even if it did work in theory (for local files), the S3 subsystem only works with Amazon S3, uses v3 of the protocol (we're on v4), and the required library cannot be installed.
For now, upload your files somewhere else (e.g imgur) and link to them.
Presuming the forum goes ok we'll write our own 💪
The first month will be invite-only. If everything is going well at that point, things will open up a bit (exact details to be discussed).
I am quite enjoying this so far, and, hopefully, so are you!