Add note about pillow version

Erotemic · Erotemic · commit 398d44d2199a · 2020-01-13T13:32:00.000-05:00
diff --git a/requirements/runtime.txt b/requirements/runtime.txt
@@ -6,4 +6,6 @@ six
 terminaltables
 torch>=1.1
 torchvision
+
+# need older pillow until torchvision is fixed
 Pillow<=6.2.2
