Document the lack of debugging support in Using the web editor

The editor debugger protocol is not implemented yet in HTML5.

(cherry picked from commit 2eedf45fde25ea5850725e390d15621331a4cbe4)

getting_started/editor/using_the_web_editor.rst

@@ -47,6 +47,9 @@ are currently missing:
 
 - No C#/Mono support.
 - No GDNative support.
+- No debugging support. This means GDScript debugging/profiling, live scene
+  editing, the Remote Scene tree dock and other features that rely on the debugger
+  protocol will not work.
 - No project exporting. As a workaround, you can download the project source
   using **Project > Tools > Download Project Source** and export it using a
   `native version of the Godot editor <https://godotengine.org/download>`__.