README: update lifecycle callback names

Author: ebidel

README.md

@@ -111,8 +111,8 @@ Example:
 The Custom Elements specification is still under discussion. The polyfill implements certain features in advance of the specification. In particular, the lifecycle callback methods that get called if implemented on the element prototype:
 
 * `createdCallback()` is called when a custom element is created.
-* `enteredDocumentCallback()` is called when a custom element is inserted into a DOM subtree.
-* `leftDocumentCallback()` is called when a custom element is removed from a DOM subtree.
+* `enteredViewCallback()` is called when a custom element is inserted into a DOM subtree.
+* `leftViewCallback()` is called when a custom element is removed from a DOM subtree.
 * `attributeChangedCallback(attributeName)` is called when a custom element's attribute value has changed
 
 `createdCallback` is invoked _synchronously_ with element instantiation, the other callbacks are called _asyncronously_. The asynchronous callbacks generally use the MutationObserver timing model, which means they are called before layouts, paints, or other triggered events, so the developer need not worry about flashing content or other bad things happening before the callback has a chance to react to changes.