Add information that pyi files are used in runtime when use attach_stub (#47)

Author: Czaki

README.md

@@ -77,7 +77,15 @@ Except that all subpackages (such as `rank`) and functions (such as `sobel`) are
 Static type checkers and IDEs cannot infer type information from
 lazily loaded imports. As a workaround you can load [type
 stubs](https://mypy.readthedocs.io/en/stable/stubs.html) (`.pyi`
-files) with `lazy.attach_stub`.
+files) with `lazy.attach_stub`:
+
+```python
+import lazy_loader as lazy
+__getattr__, __dir__, _ = lazy.attach_stub(__name__, "subpackages.pyi")
+```
+
+Note that, since imports are now defined in `.pyi` files, those
+are not only necessary for type checking but also at runtime.
 
 The SPEC [describes this workaround in more
 detail](https://scientific-python.org/specs/spec-0001/#type-checkers).