Update comment

CM2005 Object Oriented Programming/Topic 1/1.7.1/main.cpp

@@ -23,4 +23,7 @@ int main()
   int c = difference(10, 7);
   std::cout << c << std::endl;
   return 0;
-}
+}
+
+//This can be compiled adding both files as in
+//g++ main.cpp side.cpp