add video to Cant Believe Its Not Butter

Author: maiamcc

_data/dances.yml

@@ -454,6 +454,7 @@
   difficulty: accessible
   comp_notes: "It's basically \"Butter\" by Gene Hubert, only... not! (This dance is quite similar to an earlier dance independently derived by Julian Blechner, \"Page's Chain\".)"
   date_written: 201808
+  video_link: https://www.youtube.com/watch?v=reNr6ur56Hw
   blurb: "Gene Hubert's \"Butter\" but make it a larks' right-hand chain"
   choreo:
     a1: