diff --git a/pyspark/Dockerfile b/pyspark/Dockerfile
index 3ad2140..608f390 100644
--- a/pyspark/Dockerfile
+++ b/pyspark/Dockerfile
@@ -3,6 +3,7 @@
 
 # Ideally we should run as a non-root user, but it's problematic to set
 # up shared files, especially if running Docker within, say, VirtualBox.
+# See https://vsupalov.com/docker-shared-permissions/
 # ARG NB_USER="pyspark"
 # ARG NB_UID="1000"
 # ARG NB_GID="1000"