Mention the source of truth for the values (#1579)

Small follow-up to #1541 now
that the more long-term
https://github.com/NixOS/org/blob/main/doc/values.md exists.

The intention is that people don't update the values by making a PR to
the homepage, but rather the other repo.

Author: infinisil

src/pages/values.astro

@@ -8,6 +8,8 @@ import Divider from "../components/layout/Divider.astro";
 
 import Citation from "../components/ui/Citation.astro";
 import Quotation from "../components/ui/Quotation.astro";
+
+// The source of truth for this document is https://github.com/NixOS/org/blob/main/doc/values.md.
 ---
 
 <Layout title="Values">