Adjust section heading for macros in Honu.

Previously, this showed up as the first search hit
for "macros" in the Racket docs. With this change, the
Guide entry shows up first.

pkgs/honu/scribblings/honu.scrbl

@@ -188,7 +188,7 @@ An @deftech{expression} can be one of the following
   @codeblock|{(1 + 1) * 2}|}
 ]
 
-@section{Macros}
+@section{Macros in Honu}
 
 @subsection{Honu syntax}
 A good concrete syntax for honu macros is still under development.