Document unpacked extension installation through dragging and dropping

onto chrome://extensions.

BUG=282710
NOTRY=true

Review URL: https://codereview.chromium.org/81953003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@281891 0039d316-1c4b-4281-b951-d872f2087c98

chrome/common/extensions/docs/templates/articles/getstarted.html

@@ -203,6 +203,11 @@
   </li>
 </ol>
 
+<p>
+  Alternatively, you can drag and drop the directory where your extension files
+  live onto <code>chrome://extensions</code> in your browser to load it.
+</p>
+
 <p>
   If the extension is valid, it'll be loaded up and active right away! If it's
   invalid, an error message will be displayed at the top of the page. Correct