Add text under the logo on the first screen

Per https://github.com/WhisperSystems/Signal-Desktop/pull/1097#issuecomment-287477960

options.html

@@ -13,10 +13,10 @@
         <div class='inner'>
           <div class='step-body'>
             <img id='signal-icon' src='/images/icon_250.png'/>
-          </div>
-          <div class='nav'>
             <h1>{{ installWelcome }}</h1>
             <p>{{ installTagline }}</p>
+          </div>
+          <div class='nav'>
             <div> <a class='button step2'>{{ installGetStartedButton }}</a> </div>
             <span class='dot step1 selected'></span>
             <span class='dot step2'></span>