diff --git a/sdk_container/src/third_party/coreos-overlay/README.md b/sdk_container/src/third_party/coreos-overlay/README.md
index 8103b36128..cc6c1f2a69 100644
--- a/sdk_container/src/third_party/coreos-overlay/README.md
+++ b/sdk_container/src/third_party/coreos-overlay/README.md
@@ -1,7 +1,32 @@
-This overlay contains CoreOS specific packages and Gentoo packages
+# Overview
+
+This overlay contains Container Linux specific packages and Gentoo packages
 that differ from their upstream Gentoo versions.
 
+See the [portage-stable](https://github.com/coreos/portage-stable) repo
+for packages which do not have Container Linux specific changes.
+
 Licensing information can be found in the respective files, so consult
 them directly. Most ebuilds are licensed under the GPL version 2.
 
 Upstream Gentoo sources: https://gitweb.gentoo.org/repo/gentoo.git
+
+# Important packages
+
+`coreos-base/coreos` is the package responsible for everything that gets
+built into a production image and is not OEM specific.
+
+`coreos-base/coreos-dev` is the package responsible for everything that
+gets built into a developer image and is not OEM specific.
+
+`coreos-devel/sdk-depends` is the package responsible for everything that
+gets built into the Container Linux SDK.
+
+`coreos-devel/board-packages` is everything that could be built into a
+development or production image, plus any OEM specific packages.
+
+`coreos-base/oem-*` are the OEM specific packages. They mostly install things
+that belong in the OEM partition. Any RDEPENDS from these packages should
+be copied to the RDEPENDS in `board-packages` to ensure they are built.
+
+`coreos-base/coreos-oem-*` are metapackages for OEM specific ACIs.