Rework the showcase section

[bep]

See https://discourse.gohugo.io/t/cool-sites-that-run-hugo/36815/22?u=bep

The current approach where we invite site owners to "write a little story about their Hugo experience" doesn't scale well.

So I suggest we keep the layout as it is now, but make the process more lenient.

I suggest that we make it a dugnad and pick, lets say, 10 sites from https://discourse.gohugo.io/t/cool-sites-that-run-hugo/36815/21 -- and when we have agreed on that list in this thread, we can split it between us and:

1. Do a hugo new content/en/showcase/cool-site
2. Create a screenshot
3. Write a short neutral about description about the site/company.
4. Also, we should spread these out, so add a publishDate some time in the future.