added mod_expires setup

doc/setup_apache.txt

@@ -88,11 +88,26 @@ B. Edit /etc/apache2/apache2.conf
 
 C. Edit /etc/apache2/sites-enabled/000-default.conf
 
-TODO: use mail alias:
+    1.Define the document root
+    
+    TODO: use mail alias:
 
         ServerAdmin webmaster@localhost
         DocumentRoot /srv/doi/osug-doi/www
 
+    2. Add mod_expires directives:
+        # mod_expires:
+        # enable expirations
+        ExpiresActive On
+
+        ExpiresDefault "access plus 1 week"
+        ExpiresByType text/html "access plus 1 day"
+
+    3. Enable mod_expires:
+        a2enmod expires
+        service apache2 restart
+
+
 D. Customize logrotate on debian
    Debian 8 uses logrotate daily with 14 days only !