This goes over the rationale for why we need a new diff file format,
answers questions about the whys and hows, and includes a specification
for the format itself.

The spec is not complete. It's an iteration over what we had on
Hackpad/Notion, but additional changes will be coming to address things
like the metadata format and to include more examples.

Built the docs and read through them. This is still early stages, so a

lot needs to be verified during review and after.