Improve "how to think haskell"

VL1/content/VL1_how_to_think_haskell.tex

@@ -15,4 +15,5 @@
 \end{itemizep}
 \item solve atomic parts of general problems and combine them into greater solutions
 \item don't be afraid of recursion!
+\item write less, think more!
 \end{itemizep}