add a section about 'Scenes', see #88

Author: jessegreenberg

doc/phet-software-design-patterns.md

@@ -19,6 +19,7 @@ For general information on many standard design patterns, see _[Learning JavaScr
 * [Namespace](https://github.com/phetsims/phet-info/blob/master/doc/phet-software-design-patterns.md#namespace)
 * [Observer](https://github.com/phetsims/phet-info/blob/master/doc/phet-software-design-patterns.md#observer) 🚧
 * [Options and Config](https://github.com/phetsims/phet-info/blob/master/doc/phet-software-design-patterns.md#options-and-config)
+* [Scenes](https://github.com/phetsims/phet-info/blob/master/doc/phet-software-design-patterns.md#scenes)
 * [Singleton](https://github.com/phetsims/phet-info/blob/master/doc/phet-software-design-patterns.md#singleton)
 * [State Machine](https://github.com/phetsims/phet-info/blob/master/doc/phet-software-design-patterns.md#state-machine)
 * [Strategy](https://github.com/phetsims/phet-info/blob/master/doc/phet-software-design-patterns.md#strategy)
@@ -811,6 +812,17 @@ mindful of the option naming to make sure that you don't cause name collisions.
 Try to keep related options groups together, both for instantiation and `merge` statements. For examples, if you
 have several options related to a11y, keep them together, don't interleave them with other options.
 
+### Scenes
+
+Author: @jessegreenberg
+
+A "Scene" in a PhET simulation is a collection of elements presented to the user. When a new scene is selected,
+elements of the previous scene will be swapped out for elements in the new scene. A single simulation Screen may have
+multiple Scenes. The implementation of a Scene should adhere to the [Model-View-Controller (MVC)](https://github.com/phetsims/phet-info/blob/master/doc/phet-software-design-patterns.md#model-view-controller-mvc)
+pattern and be implemented like any other component in a simulation. There is no base class called Scene which
+combines a SceneModel and a SceneView. Instead, model information for a Scene should exist with the rest of the
+simulation model and view code for a scene should exist with the rest of the simulation view code.
+
 ### Nesting
 
 If using composition for your class, and you want to pass options into a subcomponent, you can nest