Update producer.tex

Author: aalvesan

sections/producer.tex

@@ -38,7 +38,7 @@ \section{Writing a Producer}\label{sec:producer}
 Note that to perform four-vector calculations, you need to import \code{attach\_coffea\_behavior} from \code{columnflow.production.util}.
 You will need to use kinematic information from both the \code{events.Electron} and \code{events.Muon} collections and create a new column which stores your calculated invariant mass.
 
-\begin{exercise}{Writing a Producer}{}
+\begin{exercise}{Writing a Producer}{h4l/production/invariant_mass.py}
 	Write a \CCSPStlye{Producer} class which computes the four lepton invariant mass. 
 \end{exercise}