Merge pull request #440 from odoo/master

Odoo: clarification of upgrading process

Author: tianon

odoo/content.md

@@ -72,6 +72,8 @@ Please note that for plain use of mails and reports functionalities, when the ho
 
 # How to upgrade this image
 
+Odoo images are updated on a regular basis to make them use recent releases (a new release of each version of Odoo is built [every night](http://nightly.odoo.com/)). Please be aware that what follows is about upgrading from an old release to the latest one provided of the same major version, as upgrading from a major version to another is a much more complex process requiring elaborated migration scripts (see [Odoo Enterprise Upgrade page](https://upgrade.odoo.com/database/upload) or this [community project](https://doc.therp.nl/openupgrade/) which aims to write those scripts).
+
 Suppose you created a database from an Odoo instance named old-odoo, and you want to access this database from a new Odoo instance named new-odoo, e.g. because you've just downloaded a newer Odoo image.
 
 By default, Odoo 8.0 uses a filestore (located at /var/lib/odoo/filestore/) for attachments. You should restore this filestore in your new Odoo instance by running