feat: comments should show how to iterate

Commens on PR opened, issue assessed, prs that're created would benefit from 'if you update the issue, add discusssions, or leave comments, add the 'openspec:go' label to have openspec flow re-run

Is there a lightweight version, mildly formatted for conveniencec - on what intentt do we add this? KISS

The issue names no files, tests, or entry points. Start by locating where openspec-flow posts comments and handles the openspec:go label, then clarify the intended lightweight wording and rerun behavior; done means the agreed guidance is shown consistently.

Written by the indexing model from the issue text.