security: Add comment that the default IdentityCertificate copy constructor works.
diff --git a/include/ndn-cpp/security/certificate/identity-certificate.hpp b/include/ndn-cpp/security/certificate/identity-certificate.hpp
index 7ce95f9..f2b585f 100644
--- a/include/ndn-cpp/security/certificate/identity-certificate.hpp
+++ b/include/ndn-cpp/security/certificate/identity-certificate.hpp
@@ -23,6 +23,8 @@
   {
   }
 
+  // Note: The copy constructor works because publicKeyName_ has a copy constructor.
+
   /**
    * Create an IdentityCertificate from the content in the data packet.
    * @param data The data packet with the content to decode.