Add a somewhat cheeky explanation of what an integration is.

(imported from commit 76d3627333a4df04019101315c368136963887bf)

templates/zephyr/integrations.html

@@ -12,6 +12,16 @@
   <div class="span8">
     <h2>Integrations</h2>
 
+    <p>The English poet John Donne once wrote that "no man is an
+    island", and we feel the same about software. No system exists in
+    complete isolation, so we've made it easy for Humbug to connect to
+    the services you already use.</p>
+
+    <p>With the integrations below, your team can stay up-to-date on
+    code changes, issue tickets, build system results, and much
+    more. So ask not for whom the notification tolls&mdash;it tolls
+    for thee! (Or for a team member of yours, I guess.)</p>
+
     <h3>Getting started</h3>
     <p>Many of these integrations are available in
     our <a href="/api">API download</a>. They also require a