Add @export_tool_button to the documention

tutorials/scripting/gdscript/gdscript_exports.rst

@@ -486,9 +486,10 @@ for a list of parameters and their allowed values.
 If you need to create a clickable inspector button, you can use ``@export_tool_button``. 
 This would export a Callable property as a clickable button. When the button is pressed, the callable is called. 
 
-Export a button with label ``"Hello"`` and icon "Callable". When you press it, it will print "Hello world!". 
+Export a button with label ``"Hello"`` and icon ``"Callable"``. When you press it, it will print ``"Hello world!"``. 
 
 ::
+
     @tool
     extends Node3D