Add XML usage to schedule.md

docs/objects/Basalt/schedule.md

@@ -15,7 +15,7 @@ Schedules a function which gets called in a coroutine. After the coroutine is fi
 
 ### Usage
 
-* Creates a schedule which switches the color between red and gray
+Creates a schedule which switches the color between red and gray:
 
 ```lua
 local mainFrame = basalt.createFrame()
@@ -34,3 +34,18 @@ aButton:onClick(basalt.schedule(function(self)
     self:setBackground(colors.gray)
 end))
 ```
+
+Usage in XML layout:
+
+```xml
+<button text="Click me">
+    <onClick>
+        basalt.schedule(function()
+            local button = event[1]
+            button:setBackground(colors.lime)
+            os.sleep(1)
+            button:setBackground(colors.black)
+        end)()
+    </onClick>
+</button>
+```