List all the places to update when adding a dependency.

There starts to be so many places to update that it's easy to forget
one.

At least from my PoV, setup.py is the canonical place; let's not add
this list of files next to each copy of the list...

Author: anntzer

setup.py

@@ -310,6 +310,13 @@ def make_release_tree(self, base_dir, files):
     package_data=package_data,
 
     python_requires='>={}'.format('.'.join(str(n) for n in py_min_version)),
+    # When updating the list of dependencies, add an api_changes/development
+    # entry and also update the following places:
+    # - lib/matplotlib/__init__.py (matplotlib._check_versions())
+    # - requirements/testing/minver.txt
+    # - doc/devel/dependencies.rst
+    # - .github/workflows/tests.yml
+    # - environment.yml
     install_requires=[
         "contourpy>=1.0.1",
         "cycler>=0.10",