diff --git a/contributing.md b/contributing.md
index 0779becbd89..9bf22269e5c 100644
--- a/contributing.md
+++ b/contributing.md
@@ -64,7 +64,7 @@ the structure of the code and of the repository.
   https://github.com/plotly/plotly.py/issues/1965. If you have writing skills,
   the wording of existing examples can also be improved in places.
 
-Contributing code or documentation are not the only way to contribute! You can
+Contributing code or documentation is not the only way to contribute! You can
 also contribute to the project by
 
 - reporting bugs (see below).
@@ -151,7 +151,12 @@ complete installation and avoid gdal-config errors.
 ```
 This will ensure that the installed packages links to your local development
 directory, meaning that all changes you make reflect directly in your
-environment (don't forget to restart the Jupyter kernel though!).
+environment (don't forget to restart the Jupyter kernel though!). For more
+information see the
+[`setuptools`](https://setuptools.readthedocs.io/en/latest/setuptools.html#development-mode)
+and
+[`pip`](https://pip.pypa.io/en/stable/reference/pip_install/#install-editable)
+documentation on _development mode_.
 
 ### ipywidgets development install
 
diff --git a/packages/python/plotly/optional-requirements.txt b/packages/python/plotly/optional-requirements.txt
index 9886dcd1872..1fcf7939d9b 100644
--- a/packages/python/plotly/optional-requirements.txt
+++ b/packages/python/plotly/optional-requirements.txt
@@ -25,6 +25,7 @@ psutil
 
 ## code formatting
 pre-commit
+black
 
 ## codegen dependencies ##
 inflect