Upgrading Symfony is easy, but I'm not sure everyone realizes this.

http://symfony.com/blog/upgrading-your-symfony-projects-the-easy-way

I propose a quick (because it's easy!) cookbook article about upgrading Symfony:

A) How to upgrade a patch release e.g. 2.5.1 to 2.5.2 (e.g.composer update symfony/symfony).

B) How to upgrade a minor release e.g. 2.5.1 to 2.6.0

C) Details on how to handle dependency issues - i.e. if you try to upgrade to a new version of Symfony, but some other dependency you have is tied to the older version.

D) Other changes you'll need to make - i.e. check the UPGRADE file.... but really, nothing needs to be changed between versions.