Add disclaimer about difference between changelog and compat dates

Author: GregBrimble

src/content/docs/workers/platform/changelog/index.mdx

@@ -13,6 +13,10 @@ description: Review recent changes to Cloudflare Workers.
 
 import { ProductChangelog } from "~/components";
 
+This changelog details meaningful changes made to Workers across the Cloudflare dashboard, Wrangler, the API, and the workerd runtime. These changes are not configurable.
+
+This is *different* to the [compatibility dates of workerd](/workers/configuration/compatibility-dates/) which specifically gate individual runtime features and can be opted-in to or out from.
+
 {/* <!-- Actual content lives in /src/content/changelogs/workers.yaml. Update the file there for new entries to appear here. For more details, refer to https://developers.cloudflare.com/style-guide/documentation-content-strategy/content-types/changelog/#yaml-file --> */}
 
 <ProductChangelog />