diff --git a/scripts/ci.requirements.txt b/scripts/ci.requirements.txt
index 18b40ec..338b14f 100644
--- a/scripts/ci.requirements.txt
+++ b/scripts/ci.requirements.txt
@@ -1,5 +1,9 @@
 # Python package requirements for Mbed TLS testing.
 
+# Any package used by a script in this repository must be listed here
+# or in one of the included files. Normally there should be a minimum
+# version constraint; the CI will test with the minimum version.
+
 # Use a known version of Pylint, because new versions tend to add warnings
 # that could start rejecting our code.
 # 2.4.4 is the version in Ubuntu 20.04. It supports Python >=3.5.