Clarify that bundle extras should not be used for PyPi installs

The bundle extras we have are only used for development and they
should not be used to install airflow from PyPI. This update
to documentation clarifies it.

Closes: apache#23692

docs/apache-airflow/extra-packages-ref.rst

@@ -294,7 +294,12 @@ Those are extras that provide support for integration with external systems via
 Bundle extras
 -------------
 
-Those are extras that install one ore more extras as a bundle.
+Those are extras that install one ore more extras as a bundle. Note that those extras should only be used for "development" version
+of Airflow - i.e. when Airflow is installed from sources. Because of the way how bundle extras are constructed they might not
+work when airflow is installed from 'PyPI`.
+
+If you want to install Airflow from PyPI with "all" extras (which should basically be never needed - you almost never need all extras from Airflow),
+you need to list explicitly all the non-bundle extras that you want to install.
 
 +---------------------+-----------------------------------------------------+------------------------------------------------------------------------+
 | extra               | install command                                     | enables                                                                |