tex: update composability section's listing

tex/part-practical.tex

@@ -374,9 +374,11 @@ Echo's built-in facilities in a more ergonomic manner using \texttt{return
 c.Render(http.StatusOk, "home.tmpl")}.
 
 \vspace{\parskip}
-\begin{lstlisting}[language=Go, caption={A conditional inside a Go template},
+\begin{lstlisting}[
+caption={Conditionaly enabling functionality inside a Go template based on user access level},
 label=tmplConditionals, basicstyle=\linespread{0.9}\small\ttfamily,
 backgroundcolor=\color{lstbg},
+morekeywords={if,and,end},
 ]
 {{ if and .User .User.IsLoggedIn .User.IsAdmin }}
 ...