Update plp.cgi intro comments to reflect new interfaces status.
To make it more usable out of the box, executable flag is set (so it can be
run directly) and uses interpreter from environment (/usr/bin/env should be
supported better than /usr/bin/perl).
-#!/usr/bin/perl
+#!/usr/bin/env perl
-# This script is not installed automatically, and is not needed for mod_perl
-# installations.
+# Executable to serve PLP scripts using CGI.
+# Not installed automatically, and only needed for CGI installations.
use PLP::CGI;