docs: add link to handwritten samples for google-maps-places (googleapis#13953)

Author: parthea

packages/google-maps-places/samples/README.rst

@@ -0,0 +1,12 @@
+Samples
+=======
+
+See `samples`_ for the :code:`google-maps-places` library.
+
+.. _samples: https://developers.google.com/maps/documentation/places/web-service/client-library-examples
+
+
+**Important**: When making API calls, you must include the :code:`x-goog-fieldmask` key within the :code:`metadata` argument. This key needs a `Field Mask`_. For an example of this, check out the sample code for `Place Details`_, which shows how to set the `Field Mask`_.
+
+.. _Place Details: https://developers.google.com/maps/documentation/places/web-service/client-library-examples#python_1
+.. _Field Mask: https://developers.google.com/maps/documentation/places/web-service/place-details#fieldmask