add youtube iframe

doc/man/index.html

@@ -27,6 +27,7 @@
   </center>
   <hr>
   <h1><a href="https://nick-black.com/dankwiki/index.php/Notcurses">notcurses</a> man pages (v2.0.2)</h1>
+  <iframe align="right" marginwidth="0" marginheight="0" frameborder="0" src="https://www.youtube.com/watch?v=cYhZ7myXyyg"></iframe>
   <a href="notcurses.3.html">notcurses(3)</a>—a blingful TUI library<br/>
   <h2>Executables (section 1)</h2>
   <a href="ncneofetch.1.html">ncneofetch</a>—generate low-effort posts for r/unixporn<br/>