521 edit homepage images (#565)

This closes #521

app/templates/views/signedout.html

@@ -13,9 +13,9 @@ U.S. Notify
 {% block content %}
 
 <section aria-label="Introduction">
-  <div class="grid-container usa-section usa-section--dark padding-top-4 padding-bottom-5">
+  <div class="grid-container usa-section usa-section--dark padding-y-4">
     <div class="grid-row grid-gap display-flex flex-align-center">
-      <div class="tablet:grid-col-7">
+      <div class="tablet:grid-col-8">
         <h1 class="font-serif-2xl usa-hero__heading">Send text messages to your users</h1>
         <p class="font-sans-lg margin-bottom-5">Try U.S. Notify now if you work in federal, state, or local government.
         </p>
@@ -25,9 +25,9 @@ U.S. Notify
           it before
         </div>
       </div>
-      <div class="tablet:grid-col-4 grid-offset-1">
-        <img src="{{ asset_url('images/product/proposition-illustration.png') }}"
-          alt="An illustration of notifications to a phone, a laptop, and a letter.">
+      <div class="tablet:grid-col-3 margin-x-5">
+        <img src="{{ asset_url('images/product/phone-text.png') }}"
+          alt="An illustration of notifications to a phone.">
       </div>
     </div>
   </div>