f - clarify VerifiedInvoiceRequest::keys docs

Author: jkczyz

lightning/src/offers/invoice_request.rs

@@ -433,10 +433,12 @@ pub struct VerifiedInvoiceRequest {
 
 	/// Keys used for signing a [`Bolt12Invoice`] if they can be derived.
 	///
-	/// If `Some`, then must respond with methods that use derived keys. Otherwise, should respond
-	/// with an invoice signed explicitly.
+	/// If `Some`, must call [`respond_using_derived_keys`] when responding. Otherwise, call
+	/// [`respond_with`].
 	///
 	/// [`Bolt12Invoice`]: crate::offers::invoice::Bolt12Invoice
+	/// [`respond_using_derived_keys`]: Self::respond_using_derived_keys
+	/// [`respond_with`]: Self::respond_with
 	pub keys: Option<KeyPair>,
 }