Note to never use using in header files in T07

Tutorials/T07-CppOverview/Slides/T7.tex

@@ -303,6 +303,7 @@ string s = "I'm a string";
 \end{lstlisting}
 \begin{itemize}
 \item This is similar to ``import Module'' vs ``from Module import *'' in Python
+\item {\bf NEVER bring namespaces into scope with \texttt{using} in header files -- this will expose the namespace in all files that use the header}
 \end{itemize}
 \end{frame}