f msg docs

Author: TheBlueMatt

lightning/src/blinded_path/message.rs

@@ -406,7 +406,8 @@ pub enum OffersContext {
 		///
 		/// Payment metadata is stored as a map from a numeric key to an arbitrary byte array value.
 		/// This allows for several types of metadata to be stored attached to a single payment. In the
-		/// future some optional features of LDK may use some keys.
+		/// future some optional features of LDK may use some keys. For the sake of conflict
+		/// reduction, those features will attempt to use keys in the range 128-256.
 		///
 		/// Note that because this is included in the payment onion, its size must be tightly
 		/// constrained. More than a few hundred bytes and the payment will be entirely unpayable (with