Update readme unpkg link on each deploy

Editor assessment

The subject states the automation plainly: the readme's unpkg link is refreshed on each deploy. chore(readme) pairs the housekeeping type with the file-derived scope, which is informative. No body or footer, and none is needed for a self-describing build step whose cadence is the whole point; the pull number gives provenance. Wording is imperative and compact. Proportionate and complete for a release-engineering touch.