Add information that pyi files are used in runtime when use attach_stub

Author: Czaki

README.md

@@ -79,6 +79,15 @@ 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`.
 
+```python 
+import lazy_loader as lazy
+__getattr__, __dir__, _ = lazy.attach_stub(__name__, "subpackages.pyi")
+```
+
+In such scenario the `lazy_loader` determine imports base on `.pyi`, 
+so `.pyi` files are then required not only for type checking but also in runtime. 
+(during freezing app that uses library using `lazy_loader` it is required to collect also `.pyi` files)
+
 The SPEC [describes this workaround in more
 detail](https://scientific-python.org/specs/spec-0001/#type-checkers).