Cause ya don't have to say it

...and where/how does the religion encourage it? Or perhaps it's so obvious that it promotes peace that no one even has to say it.

Religions promote or condemn violence to various degrees. If a holy book says "kill people" and a follower kills people, it's because of his religion, but if a holy book says "don't kill people" and a follower kills people, it's because of his own dispositions or circumstances.

For all intents and purposes you can include buddhism in that list. There certainly aren't outright calls to violence in the suttas although to be fair buddhists are not complete pacifists like the Jains (and I don't think you technically have to be vegetarian as a buddhist either). If you're going to make a category "religions of peace" I think any reasonable person would include buddhism because of it's "doctrines" and means of spiritual growth, and although Zen was the religion of the samurai and the kamikaze pilots and there are buddhists in the world who commit violent acts there is technically no justification for violence within the religion.