Homepage: link directly to top quickstarts (#325)

- By adding the top 5 languages, about 75% of quick-start users will be able to link directly to their target pages
- Language quick-starts are ordered with the most visited first
- Closes #324

layouts/partials/home/hero.html

@@ -7,14 +7,33 @@
         {{ site.Params.description }}
       </p>
 
-      <br />
-
       <div class="buttons are-medium is-centered">
         <a class="button is-primary has-text-weight-bold" href="/docs/what-is-grpc/introduction">
           Learn more
         </a>
-        <a class="button is-primary has-text-weight-bold" href="/docs/quickstart">
+      </div>
-          Get started
+
+      <br />
+
+      <p class="title is-size-3 is-size-4-mobile">Get started!</p>
+      <div class="buttons are-medium is-centered">
+        <a class="button is-primary" href="/docs/languages/go/quickstart">
+          Go
+        </a>
+        <a class="button is-primary" href="/docs/languages/cpp/quickstart">
+          C++
+        </a>
+        <a class="button is-primary" href="/docs/languages/java/quickstart">
+          Java
+        </a>
+        <a class="button is-primary" href="/docs/languages/python/quickstart">
+          Python
+        </a>
+        <a class="button is-primary" href="/docs/languages/csharp/quickstart">
+          C#
+        </a>
+        <a class="button is-primary" href="/docs/languages">
+          <i class="fas fa-ellipsis-h"></i>
         </a>
       </div>
     </div>