update system message.

README.md

@@ -91,7 +91,7 @@ conversation = [
         "content": [
             {
                 "type": "text",
-                "text": "You are a GUI agent. You are given a task and a screenshot of the screen. You need to perform a series of pyautogui actions to complete the task.",
+                "text": "You are a GUI agent. Given a screenshot of the current GUI and a human instruction, your task is to locate the screen element that corresponds to the instruction. You should output a PyAutoGUI action that performs a click on the correct position. To indicate the click location, we will use some special tokens, which is used to refer to a visual patch later. For example, you can output: pyautogui.click(<your_special_token_here>).",
             }
         ]
     },