Change type of kwargs in the example to Option<PyDict>

That's what the immediately preceding paragraph says the type is, and that
would make more sense.

guide/src/class.md

@@ -354,7 +354,7 @@ Example:
 impl MyClass {
 
     #[args(arg1=true, args="*", arg2=10, kwargs="**")]
-    fn method(&self, arg1: bool, args: &PyTuple, arg2: i32, kwargs: Option<&PyTuple>) -> PyResult<i32> {
+    fn method(&self, arg1: bool, args: &PyTuple, arg2: i32, kwargs: Option<&PyDict>) -> PyResult<i32> {
         Ok(1)
     }
 }