CODECHECK bundles

This is probably most relevant to the "default implementation" of the principles:

- How do we define a CODE CHECK bundle? Is there a need for a formal specification, or can we go the REED-way and say: a CODE CHECK bundle is a set of files that is preproducible.
- If we define a bundle
- add content to the website how to _manually_ inspect it
- add documentation about opening it with Binder

Start by resolving whether a CODECHECK bundle needs a formal specification or can be defined as a reproducible set of files. Then determine where the website guidance belongs, including instructions for manual inspection and opening bundles with Binder. Done means the bundle definition and both documentation needs are agreed and documented.

Written by the indexing model from the issue text.