Add commands docs.

TBR=finnur@chromium.org

Review URL: https://chromiumcodereview.appspot.com/10832132

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@150032 0039d316-1c4b-4281-b951-d872f2087c98

chrome/common/extensions/docs/static/experimental.commands.html

+<div id="pageData-name" class="pageData">Commands</div>
+
 <!-- BEGIN AUTHORED CONTENT -->
+
 <p>
 The commands API allows you to add keyboard shortcuts that trigger actions in
 your extension. An action can be opening the browser action or page action popup