update github link

Author: Ivan Leider

index.html

@@ -81,7 +81,7 @@
                     </div>
                 </div>
                 <div class="m-buttons">
-                    <a href="https://github.com/firecracker-microvm" class="css-button sta-hoverOFF">
+                    <a href="https://github.com/firecracker-microvm/firecracker" class="css-button sta-hoverOFF">
                         <i class="icon-github" aria-hidden="true"></i>
                         <span>join our github community</span>
                     </a>