README: add another blog post

[leonklingele]

We were using k3sup for a university project and wrote a blog post
about it :)

[derek]

Thank you for your contribution. I've just checked and your commit doesn't appear to be signed-off. That's something we need before your Pull Request can be merged. Please see our contributing guide.
Tip: if you only have one commit so far then run: git commit --amend --signoff and then git push --force.

[alexellis]

Thanks for the PR and for writing the post, you might also like arkade and inlets which are pinned on my profile :-)