Improve contribution process

[janhohenheim]

Per written feedback in our last survey, comments on Reddit, and discussions on Discord, people find the current contribution process too cumbersome.
One reason is the long time needed to clone the repo (#636), but the process of using a PR to add content in general has been questioned too.

I'm open to any suggestions for how to do this in the future.

One possibility is to allow users to submit issues to the repo and automatically generate the respective markdown in the post. This would be massively easier for contributors, but it's unclear how an editor would work with this. A possibility would be to edit the original post directly, but this does not generate a diff and is not very transparent. But maybe this tradeoff is okay?
In any case, this system would still need to be implemented by someone.