This is easy solution how to automaticaly add "www" on web page. Put the following code to your .htaccess file.
RewriteEngine on
RewriteBase /
RewriteCond %{HTTP_HOST} ^[a-z|\-]+\.[a-z]+$ [nc]
RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [L,r=301,nc]