Restore or repoint the missing getting-started quieting-warnings doc referenced by the RAG dev-warm hint

RagLogQuieting.incubatorHint emits a runtime, user-facing hint string telling users to see 'getting-started, "Quieting startup warnings"', but no getting-started.adoc and no such section exist under docs/. The R483 audit removed the stale javadoc pointer to it, but the emitted message string still points at a nonexistent doc, so a user who follows the hint lands nowhere. Because it is a user-facing message string rather than a comment, the comment-drift tools do not apply; the fix is either to author the getting-started "Quieting startup warnings" section or to repoint the hint at an existing doc, a doc/behavior change that warrants its own item.

Surfaced by the R483 javadoc drift audit.