doc: fix broken link on howto/unicode page (#13160)

Thank you @redshiftzero on the first PR 👏 

Doc/howto/unicode.rst

@@ -157,7 +157,7 @@ difficult reading.  `A chronology <http://www.unicode.org/history/>`_ of the
 origin and development of Unicode is also available on the site.
 
 On the Computerphile Youtube channel, Tom Scott briefly
-`discusses the history of Unicode and UTF-8 <https://www.youtube.com/watch?v=MijmeoH9LT4>`
+`discusses the history of Unicode and UTF-8 <https://www.youtube.com/watch?v=MijmeoH9LT4>`_
 (9 minutes 36 seconds).
 
 To help understand the standard, Jukka Korpela has written `an introductory