Add watch intro class

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

Author: alexellis

_includes/landing-page/yt-player/youtube.html

@@ -1,5 +1,5 @@
 <div class="yt-player-container">
-    <div class="yt-player-iframe-wrapper">
+    <div class="yt-player-iframe-wrapper ready">
         <a href="https://www.youtube.com/watch?v=ZnZJXI377ak">
         <video id="sample-video" muted loop autoplay poster="{{ site.baseurl }}/images/openfaas/yt-cover.jpg">
             <source src="{{ site.baseurl }}/videos/landing-video.mp4" type="video/mp4">