comment why we use an unreleased version of python kubernetes

requirements.in

@@ -15,7 +15,11 @@
 ansible<2.10
 # needed for test_dns.py
 dnspython
-# kubernetes -- We need an unreleased version for install/generate_secrets.py (post 13814c0f7e0e587c46512386da3d08c64fc83e04), so we install from git directly:
+# `install/generate_secrets.py` needs the `create_from_yaml` function that accepts
+# the `yaml_objects` parameter which was added in commit
+# 13814c0f7e0e587c46512386da3d08c64fc83e04. Until that is merged into a stable
+# release, we install from Git. Should be replaced with `kubernetes>18` some time
+# in the future.
 -e git+git://github.com/kubernetes-client/python.git@2f9643eac71535f7802cd16a078ce50e8866f1ad#egg=kubernetes
 # Needed for testinfra using the ansible module
 paramiko