Describe this example, and add stricture.

docs/eg-10-setup.pl

@@ -1,4 +1,6 @@
-#!/usr/bin/perl
+#!/usr/bin/env perl
+
+# Exercise the new "setup" option for Emitter and Observer traits.
 
 {
 	package Counter;
@@ -48,6 +50,9 @@
 	}
 }
 
+use warnings;
+use strict;
+
 my $w = Watcher->new();
 Stage->run_all();
 exit;