Add contributing guide to README

[pr130]

step by step instructions for jupyter notebooks and R markdown (HTML output)

[KonradUdoHannes]

We should probably also have a section for how to contribute/preview the notebook/md file itself. I see two relevant aspects here access and the ability to preview the post. My topmost aim here would be to get as many Correlaiders involved as possible. Should the be so much interest that maintenance of the suggested processes becomes to much of an issue I would already consider it a success and address that issue then.

Without preview

• get invited to the repo and commit a notebook/md
• for the repository and send a pull request with a notebook/md
• A compromise would be to use githubs branch protection to restrict access to the master and gh-pages branch. This would allow to more generously give access to the repo itself and have users contribute safely within branches. It replaces a fork/pull request workflow with a branch workflow. Not sure which one is easier of new users.

Preview options

• No Preview. The default formatting should be good enough that people feel ok submitting simple notebooks without the need for huge previews
• Assurance of the ability to update the post. We should probably stress that we'll help to update posts afterwards.
• Docker compose local server
• Personal FastPages blog

Any other ideas at the moment?