Improve the documentation of the RFC process

[lubianat]

This is a first step towards.

• Generating the RFC index German-BioImaging/ome-zarr-ideas#54
• Clarify comment/review and avoiding "dev" versions of RFCs German-BioImaging/ome-zarr-ideas#55

It may include

• A table documenting the RFC codes - Improve the documentation of the RFC process  #397
• a minor update to the wording of R2 in the spec.
• An FAQ to onboard people in general
• Automation around building the RFC index
• Improved findability of Comments, Reviews, Responses and Versions for RFCs
• Improved findability of issues, prs and repositories related to a particular OME-Zarr RFC

Other ideas are welcome.

[lubianat]

from the duplicated issue:

• fix weird anchors

• improve links to posts on image.sc

also see

• Writing the missing RFC pages in forum.image.sc German-BioImaging/ome-zarr-ideas#37