update utils docs

docs/reference/utils/utils.md

@@ -1,8 +1,25 @@
 
 # Utils
 
-These are extra utility functions that ship with Slate that may be useful for certain use cases.
+```js
+import {
+  findDOMNode,
+  setKeyGenerator
+} from 'slate'
+```
 
+Utility functions that ship with Slate that may be useful for certain use cases.
+
+- [`findDOMNode`](#finddomnode)
+- [`setKeyGenerator`](#setkeygenerator)
+
+
+## Functions
+
+### `findDOMNode`
+`findDOMNode(key: String) => DOMElement`
+
+Allows you to find the DOM node for a Slate [`Node`](../models/node.md) by passing its `key` string. Modelled after React's built-in `findDOMNode` helper.
 
 ### `setKeyGenerator`
 `setKeyGenerator(generator: Function) => Void`