add utils reference

docs/Summary.md

@@ -47,6 +47,11 @@
 - [Core](./reference/plugins/core.md)
 
 
+## Utils Reference
+
+- [Utils](./reference/utils/utils.md)
+
+
 ## General
 
 - [FAQ](./general/faq.md)

docs/reference/Readme.md

@@ -25,3 +25,5 @@ This is the full reference documentation for all of the pieces of Slate, broken
 - **Plugins**
   - [Plugins](./plugins/plugin.md)
   - [Core](./plugins/core.md)
+- **Utils**
+  - [Utils](./utils/utils.md)

docs/reference/models/node.md

@@ -39,6 +39,15 @@
 
 ## Properties
 
+### `key`
+`String`
+
+A short-lived, unique identifier for the node.
+
+By default, keys are not meant to be long-lived unique identifiers for nodes that you might store in a database, or elsewhere. They are meant purely to identify a node inside of a single Slate instance. For that reason, they are simply auto-incrementing strings. (eg. `'0'`, `'1'`, `'2'`, ...) 
+
+If you want to make your keys uniqueness long-lived, you'll need to supply your own key generating function via the [`setKeyGenerator`](../utils/utils.md#setkeygenerator) util.
+
 ### `nodes`
 `Immutable.List`
 

docs/reference/utils/utils.md

@@ -0,0 +1,12 @@
+
+# Utils
+
+These are extra utility functions that ship with Slate that may be useful for certain use cases.
+
+
+## `setKeyGenerator`
+`setKeyGenerator(generator: Function) => Void`
+
+Allows you to specify your own key generating function, instead of using Slate's built-in default generator which simply uses auto-incrementing number strings. (eg. `'0'`, `'1'`, `'2'`, ...)
+
+This will act globally on all uses of the Slate dependency.