update readme

Author: adhami3310

README.md

@@ -15,13 +15,15 @@ pip install ruff-format
 ## Usage
 
 ```python
-from ruff_format import format_string
+from ruff_format import format_string, is_valid_syntax
 
 code = """
 def hello(  x,y,   z  ):
     print( x+y+z )
 """
 
+assert is_valid_syntax(code)
+
 formatted = format_string(code)
 print(formatted)
 ```