Add link[rel="alternate"] pointing to YouTube version

Author: notpushkin

src/invidious/views/watch.ecr

@@ -22,6 +22,7 @@
 <meta name="twitter:player" content="<%= HOST_URL %>/embed/<%= video.id %>">
 <meta name="twitter:player:width" content="1280">
 <meta name="twitter:player:height" content="720">
+<link rel="alternate" href="https://www.youtube.com/watch?v=<%= video.id %>">
 <%= rendered "components/player_sources" %>
 <title><%= HTML.escape(video.title) %> - Invidious</title>
 <% end %>