Contribute more examples

[simolus3]

We have some examples live on the documentation page, but we should have more! In particular, we're currently missing out on larger or even end-to-end examples that could be downloaded and are ready to run.

Some ideas for examples could be:

• Implementations for the 7GUIs tasks evaluating the expressiveness of GUI toolkits. I've started implementing some of them in examples/, but it would be better to have working examples in the docs.
• Examples using riverpod_zap (there's one in riverpod_zap/example which could serve as a starting point)
• Full example packages (e.g. things that could be downloaded and are ready to run). There's a project downloader in the docs, but we could expand it to different prebuilt templates. Those templates could also be more complex (e.g. depend on external Sass packages, combine multiple builders, ...).

More ideas for examples are appreciated too!

Ideally, simplify examples for the documentation should go here. If you want to setup full example projects, we could have them in a central directory (maybe examples/?).

If you want to work on this, or run into any issues setting up examples, please let me know!