add comment about why enum comparers are more complicated

src/vm/jitinterface.cpp

@@ -8745,6 +8745,9 @@ CORINFO_CLASS_HANDLE CEEInfo::getDefaultEqualityComparerClassHelper(CORINFO_CLAS
     }
 
     // Enum
+    //
+    // We need to special case the Enum comparers based on their underlying type,
+    // to avoid boxing and call the correct versions of GetHashCode.
     if (elemTypeHnd.IsEnum())
     {
         MethodTable* targetClass = NULL;