fix: fix README.md error (#99)

Author: aeeeeeep

README.md

@@ -82,8 +82,10 @@ def main():
     # Your code
     pass
 
-with objwatch.ObjWatch(['your_module.py']):
+if __name__ == '__main__':
+    obj_watch = objwatch.watch(['your_module.py'])
     main()
+    obj_watch.stop()
 ```
 
 ### Example Usage

docs/source/index.rst

@@ -91,8 +91,10 @@ Using the API
        # Your code
        pass
 
-   with objwatch.ObjWatch(['your_module.py']):
+   if __name__ == '__main__':
+       obj_watch = objwatch.watch(['your_module.py'])
        main()
+       obj_watch.stop()
 
 Example Usage
 --------------
@@ -393,4 +395,4 @@ Indices and tables
 
 * :ref:`genindex`
 * :ref:`modindex`
-* :ref:`search`
+* :ref:`search`