feat: typing support for helpers (#2588)

* feat: basic typing support

* docs: mention syncing as suggested by @rwgk

* docs: update changelog

* docs: copy of warning in limitations
diff --git a/tools/setup_main.py.in b/tools/setup_main.py.in
index c859c1f..2231a08 100644
--- a/tools/setup_main.py.in
+++ b/tools/setup_main.py.in
@@ -19,6 +19,7 @@
         "pybind11.share.cmake.pybind11",
     ],
     package_data={
+        "pybind11": ["py.typed", "*.pyi"],
         "pybind11.include.pybind11": ["*.h"],
         "pybind11.include.pybind11.detail": ["*.h"],
         "pybind11.share.cmake.pybind11": ["*.cmake"],