Document -const option.

git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk@11391 626c5289-ae23-0410-ae9c-e8d60b6d4f22

Doc/Manual/Perl5.html

@@ -815,7 +815,7 @@ extern char *path;       // Declared later in the input
 
 
 <p>
-Constants are wrapped as read-only Perl variables.  For example:
+By default, constants are wrapped as read-only Perl variables.  For example:
 </p>
 
 <div class="code">
@@ -838,6 +838,19 @@ $example::FOO = 2;           # Error
 </pre>
 </div>
 
+<p>
+Alternatively, if you use swig's <tt>-const</tt> option, constants are wrapped
+such that the leading $ isn't required (by using a constant subroutine), which
+usually gives a more natural Perl interface, for example:
+</p>
+
+<div class="targetlang">
+<pre>
+use example;
+print example::FOO,"\n";
+</pre>
+</div>
+
 <H3><a name="Perl5_nn18"></a>28.4.4 Pointers</H3>