add some comments to note the duplication between setup.py and tox.ini
diff --git a/setup.py b/setup.py
index eb1b3d3..ccb1e5f 100644
--- a/setup.py
+++ b/setup.py
@@ -40,6 +40,7 @@
     SIX_DEPENDENCY
 ]
 
+# If you add a new dep here you probably need to add it in the tox.ini as well
 test_requirements = [
     "pytest",
     "pretend",