f - expand builder docs

Author: jkczyz

lightning/src/offers/offer.rs

@@ -79,7 +79,9 @@ pub struct OfferBuilder {
 
 impl OfferBuilder {
 	/// Creates a new builder for an offer with the given description, using the given pubkey for
-	/// signing invoices.
+	/// signing invoices. The associated secret key must be remembered while the offer is valid.
+	///
+	/// Use a different pubkey per offer to avoid correlating offers.
 	pub fn new(description: String, signing_pubkey: PublicKey) -> Self {
 		let offer = OfferContents {
 			chains: None, metadata: None, amount: None, description, features: None,