minor doc update. [skip ci]

docs/guide/intro-upgrade-from-v1.md

@@ -19,24 +19,25 @@ the [Starting from Basic App](start-basic.md) chapter to learn how to install Yi
 create new extensions or turn your existing 1.1 extensions into 2.0, please refer to
 the [Creating Extensions](extend-creating-extensions.md) chapter.
 
-PHP
----
 
-Yii 1.1 was developed to be compatible with PHP 5.2. Yii 2.0 minimum requirement is PHP 5.4 that is a huge improvement
-in both performance and features. And since these features are actually used you need to get yourself familiar with them.
-Here's the list:
+PHP Requirements
+----------------
+
+Yii 2.0 requires PHP 5.4 or above, which is a huge improvement over PHP 5.2 as required by Yii 1.1.
+As a result, there are many differences at language level that you should pay attention to.
+Below is a summary of the major changes regarding PHP:
 
 - [Namespaces](http://php.net/manual/en/language.namespaces.php).
 - [Anonymous functions](http://php.net/manual/en/functions.anonymous.php).
-- Short array syntax. It's easy, just use `[` and `]` instead of `array(` and `)`.
-- Short `echo` in form of `<?=` used in framework views. In PHP 5.4 it's always available unlike
-  [`<?` that isn't safe to use](http://php.net/manual/en/language.basic-syntax.phptags.php).
-- [SPL](http://php.net/manual/en/book.spl.php).
+- Short array syntax `[...elements...]` is used instead of `array(...elements...)`.
+- Short echo tags `<?=` are used in view files. This is safe to use starting from PHP 5.4.
+- [SPL classes and interfaces](http://php.net/manual/en/book.spl.php).
 - [Late Static Bindings](http://php.net/manual/en/language.oop5.late-static-bindings.php).
 - [Date and Time](http://php.net/manual/en/book.datetime.php).
 - [Traits](http://php.net/manual/en/language.oop5.traits.php).
-- [intl](http://php.net/manual/en/book.intl.php). Yii 2.0 has many convenient wrappers for intl features in `i18n`
-  components but it is worth reading anyway to understand it better.
+- [intl](http://php.net/manual/en/book.intl.php). Yii 2.0 makes use of the `intl` PHP extension
+  to support internationalization features.
+
 
 Namespace
 ---------