Use snippets in the README

[rbehjati]

          Might make sense to link only to the file, to keep it consistent?

https://github.com/project-oak/hello-transparent-release/blob/main/.github/workflows/provenance.yaml

Or can we show snippets from a link/permalink? That would be amazing! Like here https://github.blog/2017-08-15-introducing-embedded-code-snippets/?

Originally posted by @mariaschett in #6 (comment)