Added a comment

Author: nibanks

src/core/api.h

@@ -5,6 +5,11 @@
 
 --*/
 
+//
+// Private flag of the QUIC_CONNECTION_SHUTDOWN_FLAGS enum used for indicating
+// the type of error code being passed in. Not exposed to apps because they
+// should not be using different types of errors directly.
+//
 #define QUIC_CONNECTION_SHUTDOWN_FLAG_STATUS ((QUIC_CONNECTION_SHUTDOWN_FLAGS)0x8000)
 
 _IRQL_requires_max_(PASSIVE_LEVEL)