Document temporal/geographic coverage of the v2026.08.25 snapshot.

README.md

@@ -34,6 +34,7 @@ of its own. Every status is computed from cited evidence.
   the page's trailing slash, so `/plants/{id}/` is JSON at
   `/plants/{id}.json`.
 - Snapshot: https://github.com/grysngrhm-tech/fireapproved-data/releases/tag/v2026.08.25
+- Coverage: source documents dated 1968 through 2026-08-25 (23,103 of 26,878 rows carry a document date). 112 sources in the United States, Europe, the Mediterranean, Australia, New Zealand, South America, and other named regions. Not a global flora census.
 - Methodology: https://fireapproved.com/methodology
 
 **Citation:** FireApproved.com (2026). Plant flammability evidence