Improve code docs

none/expression.py

@@ -6,6 +6,14 @@ from aiocqhttp import message
 
 def render(expr: Union[str, Sequence[str], Callable], *, escape_args=True,
            **kwargs) -> str:
+    """
+    Render an expression to message string.
+
+    :param expr: expression to render
+    :param escape_args: should escape arguments or not
+    :param kwargs: keyword arguments used in str.format()
+    :return: the rendered message
+    """
     if isinstance(expr, Callable):
         expr = expr()
     elif isinstance(expr, Sequence):