Update source/tutorials/packaging-projects.rst

Co-authored-by: Sviatoslav Sydorenko <wk.cvs.github@sydorenko.org.ua>

Author: henryiii

source/tutorials/packaging-projects.rst

@@ -51,7 +51,7 @@ project's root directory - you will add content to them in the following steps.
     │   └── __init__.py
     ├── pyproject.toml
     ├── setup.cfg
-    ├── setup.py  # optional
+    ├── setup.py  # optional, needed to make editable pip installs work
     └── tests