In defaultSign, added hint for setting the current time.
diff --git a/ndn-cpp/key-chain.hpp b/ndn-cpp/key-chain.hpp
index 2259064..1ddaa91 100644
--- a/ndn-cpp/key-chain.hpp
+++ b/ndn-cpp/key-chain.hpp
@@ -15,7 +15,8 @@
/**
* In data, set the signed info publisher public key digest and key locator key to the default public key and set the
* signature using the default private key.
- * Note: the caller must make sure the timestamp is correct with data.getSignedInfo().setTimestampMilliseconds.
+ * Note: the caller must make sure the timestamp is correct, for example with
+ * data.getSignedInfo().setTimestampMilliseconds(time(NULL) * 1000.0).
* @param data The Data object to sign and set the signature.
*/
static void defaultSign(Data &data);