diff --git a/sdk_container/src/third_party/coreos-overlay/coreos/stage1_hooks/README.md b/sdk_container/src/third_party/coreos-overlay/coreos/stage1_hooks/README.md
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+The scripts there are called when setting up the portage-stable and
+coreos-overlay repos for the stage1 build. When the scripts are
+invoked, they receive a path to the repository as a parameter. The
+script for portage-stable should end with `-portage-stable.sh`, and
+the script for coreos-overlay with '-coreos-overlay.sh`. For example
+`0000-replace-ROOTPATH-coreos-overlay.sh`.