Include Help keyboard shortcut on splash

Include keyboard shortcut hint to enable 100% no mouse usage even from the beginning. :smile:

assets/javascripts/templates/pages/root_tmpl.js.erb

@@ -32,7 +32,7 @@ app.templates.intro = `\
      Here's what you should know before you start:
   <ol class="_intro-list">
     <li>Open the <a href="/settings">Preferences</a> to enable more docs and customize the UI.
-    <li>You don't have to use your mouse &mdash; see the list of <a href="/help#shortcuts">keyboard shortcuts</a>.
+    <li>You don't have to use your mouse &mdash; see the list of <a href="/help#shortcuts">keyboard shortcuts</a> (or press '?' at anytime).
     <li>The search supports fuzzy matching (e.g. "bgcp" brings up "background-clip").
     <li>To search a specific documentation, type its name (or an abbr.), then Tab.
     <li>You can search using your browser's address bar &mdash; <a href="/help#browser_search">learn how</a>.