Add note about using src folder for packaging

Author: glentner

docs/source/tutorial/packaging.rst

@@ -322,6 +322,15 @@ like.
     )
 
 
+.. note::
+
+    Ultimately, it is highly recommended to nest your source package root with a `src`
+    directory. Doing so prevents a lot of common pitfalls you are likely to run into,
+    as discussed on
+    `good integration practices <https://docs.pytest.org/en/6.2.x/goodpractices.html>`_
+    at pytest.org, which links to an excellent
+    `blog post by Ionel Cristian Mărieș <https://blog.ionelmc.ro/2014/05/25/python-packaging/#the-structure>`_.
+
 
 Installation
 ^^^^^^^^^^^^