title: What do the --save flags do with npm install
body: <p>I see instructions to install a package with either</p>
  
  <pre><code>npm install &lt;package_name&gt;
  </code></pre>
  
  <p>or</p>
  
  <pre><code>npm install &lt;package_name&gt; --save
  </code></pre>
  
  <p>or</p>
  
  <pre><code>npm install &lt;package_name&gt; --save-dev
  </code></pre>
  
  <p>What is the difference between these options?</p>