This will add a simple widget which displays just a small message.

 add_action('wp_dashboard_setup', 'register_my_dashboard_widgets');
        
 function register_my_dashboard_widgets() {
     wp_add_dashboard_widget('myInfo_widget', 'Important Information', 'display_infoWidget');
 }
        
function display_infoWidget() {
     echo '<p>At the first of february this site gets a new design.
     Therefore is wont be available this day. To see the current progress you can visit 
     <a href="http://www.justanexample.com" >this site</a></p>';
 }