Organizational changes to this repo's layout

[kMutagene]

Upon internal discussions and following quite a lot of confusion and out-of-sync information, these repos:

• ARC-specification
• isa-ro-crate-profile
• arc-cwl-ro-crate-profile
• arc-datamap-ro-crate-profile

Will undergo a re-organization of the repo layout:

• All repos will be connected to zenodo for DOI minting (this repo is already connected, the profiles are currently not)
• A new release branch will be introduced, of which HEAD will always point to the respectively latest release tag. This means that the content of the release branch will always be in sync with the latest release, the content of the zenodo record, and the respective DOI
• The release branch will be the default branch on GitHub
• A new dev branch will be created, which is where ALL PRs other than releases must be targeted to.
• The release branch will be protected from direct pushes, and only accept PRs from the dev branch
• A small contribution guide will be added to all repos readmes

See also nfdi4plants/ARC-specification#119

[kMutagene]

Done, make sure to update or re-clone the repo to not run into branch protection rules, cc @caroott