docs: blog post on the workbook and how it is generated

Covers the purpose (calisthenics has no barbell, so standards are opinions until
someone writes them down) and the data-driven build, but the substance is the
failure modes: nearly every real bug in this project produced plausible output
rather than an error, and the habit that caught them was looking at rendered
pages instead of exit codes.

Every figure quoted is checked against the repo.
