diff --git a/docs/resources.md b/docs/resources.md
index c8ea580..40353b3 100644
--- a/docs/resources.md
+++ b/docs/resources.md
@@ -1,3 +1,7 @@
+# Preamble
+
+This file is the authoritative mapproxy resource documentation. Please, keep it in sync with the actual implemtation.
+
 # Supported resource types/drivers
 
 Mapproxy supports following resource types: