Reorganize Hello World Page (#962)

* Reorganize Hello World Page

Move codeblock to the very top and and "following along" heading

* Match tense

* Remove subheading

content/docs/hello-world.md

@@ -12,8 +12,6 @@ redirect_from:
   - "docs/getting-started-zh-CN.html"
 ---
 
-The easiest way to get started with React is to use [this Hello World example code on CodePen](codepen://hello-world). You don't need to install anything; you can open it in another tab and follow along as we go through examples. If you'd rather use a local development environment, check out the [Installation](/docs/try-react.html) section.
-
 The smallest React example looks like this:
 
 ```js
@@ -27,6 +25,10 @@ It displays a heading saying "Hello, world!" on the page.
 
 The next few sections will gradually introduce you to using React. We will examine the building blocks of React apps: elements and components. Once you master them, you can create complex apps from small reusable pieces.
 
+## Following Along
+
+The easiest way to get started with React is to use [this Hello World example code on CodePen](codepen://hello-world). You don't need to install anything; you can open it in another tab and follow along as we go through examples. If you'd rather use a local development environment, check out the [Installation](/docs/try-react.html) section.
+
 ## Knowledge Level Assumptions
 
 React is a JavaScript library, and so we'll assume you have a basic understanding of the JavaScript language. **If you don't feel very confident, we recommend [going through a JavaScript tutorial](https://developer.mozilla.org/en-US/docs/Web/JavaScript/A_re-introduction_to_JavaScript) to check your knowledge level** and enable you to follow along this walkthrough without getting lost. It might take you between 30 minutes and an hour, but as a result you won't have to feel like you're learning both React and JavaScript at the same time.