Add trailing slash to URL

[join]

I'm a newbie in web-development
How can I modify .htaccess file so that to add trailing slash to every URL?
http://www.site.com/about/ instead of http://www.site.com/about

My .htaccess file looks like:

Code:

AddDefaultCharset UTF-8
RewriteEngine on

RewriteBase /getsimple/
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule /?([A-Za-z0-9-]+)/?$ index.php?id=$1 [L]

Thanks in advance.

[pixelita]

This article should help. There is a bit of concern from some of the threads I've read on this topic about duplicate content issues, but I don't think there is too much to worry about.
http://enarion.net/web/apache/htaccess/trailing-slash/