title: 'tsc command not found' in compiling typescript
body: <p>I want to install typescript, so I used the following command:</p>
  
  <pre><code>npm install -g typescript 
  </code></pre>
  
  <p>and test <code>tsc --version</code>, but it just show 'tsc command not found'. I have tried many ways as suggested in stackoverflow, github and other sites. but it doesn't work. How could I know typescript is installed and where it is.</p>
  
  <p>my OS is Unix, OS X El Capitan 10.11.6, 
     node version is 4.4.3, 
     npm version is 3.10.5</p>