Add link to PR screencast

submit.html

@@ -60,6 +60,8 @@ <h3>Submit with R</h3>
 
 <p>You can submit posts by creating pull requests on GitHub. <a href="https://github.com/rweekly/rweekly.org">https://github.com/rweekly/rweekly.org</a></p>
 
+<p>If you're not sure how to do this you can watch <a href="https://www.youtube.com/watch?v=oNcW5xeV1bw">this short screencast</a> created by Sina Rüeger demonstrating how you can contribute a new link to the R-Weekly issue via a GitHub pull request.</p>
+
 <p>Alternatively you can suggest #rstats content you come across on Twitter by tagging @rweekly_submit in a reply as illustrated below:</p>
 <blockquote class="twitter-tweet"><p lang="en" dir="ltr">Found a link on Twitter you want to submit to <a href="https://twitter.com/rweekly_org?ref_src=twsrc%5Etfw">@rweekly_org</a>? It&#39;s now even easier! Just tag <a href="https://twitter.com/rweekly_submit?ref_src=twsrc%5Etfw">@rweekly_submit</a> in a direct reply to the tweet linking to the post and we&#39;ll consider it for the next issue. <a href="https://t.co/yiLyM9RD6S">pic.twitter.com/yiLyM9RD6S</a></p>&mdash; R Weekly Submit (@rweekly_submit) <a href="https://twitter.com/rweekly_submit/status/1265250240753328128?ref_src=twsrc%5Etfw">May 26, 2020</a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>