Added advice to include a header for each source file

Lectures/L19_AssuranceCase/AssuranceCase.tex

@@ -404,6 +404,12 @@ instructor, supervisor, users
 \ei
 %\item Your decisions on style may evolve over the project
 \item Important to be consistent
+\item Every code file should have a header with
+\begin{itemize}
+  \item Author(s)
+  \item Date
+  \item Purpose
+\end{itemize}
 \ei
 
 \end{frame}