Bug 1602735 - Update SeaMonkey website for 2.53.1 Beta 1 release - update system requirements. r=me

src/doc/system-requirements.en.html

@@ -18,7 +18,7 @@
 
 <h2 id="windows">Windows</h2>
 <div class="section">
-  <h3>Operating Systems</h3>
+  <h3>Operating Systems (32-bit and 64-bit)</h3>
   <ul>
     <li>Windows XP Service Pack 2</li>
     <li>Windows Vista</li>
@@ -27,6 +27,11 @@
     <li>Windows 8.1</li>
     <li>Windows 10</li>
   </ul>
+  <p>
+    <i>Please note that 64-bit builds of SeaMonkey are only supported on
+    Windows 7 and higher.<br>SeaMonkey 2.49.5 will be the last release to run
+    on Windows XP and Vista.</i>
+  </p>
   <h3>Minimum Hardware</h3>
   SeaMonkey on Windows needs a CPU supporting the SSE2 instruction set.
   <ul>