Tweaked the intro page

Here are some ideas that I think work better:
- 15 repetitions of "React". Removed a few.
- The "two main ideas" weren't clearly separated. I put them under different headers and simplified the wording.
- The "Give it Five Minutes section didn't sound as reassuring. Made it sound more certain.

docs/01-why-react.md

@@ -7,21 +7,23 @@ next: displaying-data.html
 ---
 React is a JavaScript library for creating user interfaces by Facebook and Instagram. Many people choose to think of React as the **V** in **[MVC](http://en.wikipedia.org/wiki/Model%E2%80%93view%E2%80%93controller)**.
 
-We built React to solve one problem: **building large applications with data that changes over time**. To do this, React has two main ideas.
+We built React to solve one problem: **building large applications with data that changes over time**. To do this, React uses two main ideas.
 
-### Stay Simple and Declarative
+### Simple
 
-React apps are easy to write. Simply express how the UI should look at any given point in time, and React will manage all UI updates for you when your underlying data changes.
+Simply express how your app should look at any given point in time, and React will automatically manage all UI updates when your underlying data changes.
 
-It's just like writing a server-rendered web app: when the data changes, React conceptually hits the refresh button, except React is very fast and maintains the state of your UI. Because of this, React's API is very small and easy to understand.
+### Declarative
+
+When the data changes, React conceptually hits the "refresh" button, and knows to only update the changed parts.
 
 ## Build Composable Components
 
 React is all about building reusable components. In fact, with React the *only* thing you do is build components. Since they're so encapsulated, components make code reuse, testing, and separation of concerns easy.
 
-## Give it Five Minutes
+## Give It a Try
 
-React challenges a lot of conventional wisdom, and at first glance some of the ideas may seem crazy. We ask that you [give it five minutes](http://37signals.com/svn/posts/3124-give-it-five-minutes) while reading about React; engineers and designers have built thousands of components both inside and outside of Facebook and Instagram, and we hope you'll find it useful!
+We solved a lot of problems through challenging conventional wisdom. [Give it Five Minutes](http://37signals.com/svn/posts/3124-give-it-five-minutes); engineers and designers have built thousands of components both inside and outside of Facebook and Instagram: those crazy ideas work.
 
 ## Learn More