Add LP2019 talk cs4m video link

Was finally published.  This year they included the slides in the video,
which is perfect, since this was a technical talk that used the slides to
demonstrate the commands, and I actually did some stuff on the computer
during the talk.

Though the PIP did slightly cut off some commands; see the PDF or Org
sources for the full commands.

src/talks.rec

@@ -51,6 +51,7 @@ abstract: Words like "wizardry" and "incantation" have long been used to describ
 + This session demonstrates a range of practical possibilities when
 + machine acts as an extension of the user's imagination, for the technical
 + and nontechnical alike.
+video-url: https://media.libreplanet.org/u/libreplanet/m/computational-symbiosis-methods-that-meld-mind-and-machine/
 link: /talks/cs4m.pdf Slides
 link: /projects/cs4m/ Source Code
 event-link: https://libreplanet.org/2019