[#3404] Better description of change

- Detailed the reason for the change, provided code samples of affected an
  unaffected code, and expanded descriptions.

README.md

@@ -7,20 +7,58 @@ Develop: [![Build Status](https://secure.travis-ci.org/zendframework/zf2.png?bra
 
 *Zend Framework 2.1.0dev*
 
-This is the first minor (feature) release for the 2.0 series.
+This is the first minor (feature) release for the version 2 series.
 
 DD Mmm YYYY
 
 ### UPDATES IN 2.1.0
 
 #### Backwards Compatibility Break: Session Storage
-The default session storage object has changed to an array adapter; this
-is a minimal break in compatibility.  Most developers are not working
-directly with the storage object, but rather a Container, therefore switching
-out the default will not change anything for those developers.
-For those who are using it directly:
- * Register the old SessionStorage object explicitly, or
- * Do not utilize object notation for accessing members of the Storage object.
+
+The default session storage object has changed from
+`Zend\Session\Storage\SessionStorage` to an array adapter
+(`Zend\Session\Storage\SessionArrayStorage`; this is a minimal break in
+compatibility.  Most developers are not working directly with the storage
+object, but rather a `Zend\Session\Container`; as a result, switching out the
+default will not cause compatibility problems for most developers.
+
+The change was introduced to alleviate issues when working with 3rd party
+libraries that access nested members of the `$_SESSION` superglobal.
+
+Those affected will be those (a) directly accessing the storage instance, and
+(b) using object notation to access session members:
+
+```php
+    $foo = null;
+
+    /** @var $storage Zend\Session\Storage\SessionStorage */
+    if (isset($storage->foo)) {
+        $foo = $storage->foo;
+    }
+```
+
+If you are using array notation, as in the following example, your code remains
+forwards compatible:
+
+```php
+    $foo = null;
+
+    /** @var $storage Zend\Session\Storage\SessionStorage */
+    if (isset($storage['foo'])) {
+        $foo = $storage['foo'];
+    }
+```
+
+If you are not working directly with the storage instance, you will be
+unaffected.
+
+For those affected, the following courses of action are possible:
+
+- Update your code to replace object property notation with array notation, OR
+- Initialize and register a `Zend\Session\Storage\SessionStorage` object
+  explicitly with the session manager instance.
+
+#### Other updates in 2.1.0
 
 Please see CHANGELOG.md.