Add link to Quarto Drop extension for reveal.js (#1273)

Author: georgestagg

docs/extensions/listings/revealjs.yml

@@ -53,6 +53,12 @@
   description:
     A plugin that lets you step through fragments and code higlights at the same time. 
 
+- name: drop
+  path: https://github.com/r-wasm/quarto-drop
+  author: "[George Stagg](https://github.com/georgestagg)"
+  description:
+    Drop down an interactive R or Python console, code editor, and plotting window from the top of your slides.
+
 - name: reveal-header
   path: https://github.com/shafayetShafee/reveal-header
   author: "[Shafayet Khan Shafee](https://github.com/shafayetShafee)"