diff --git a/doc/stacker_yaml.md b/doc/stacker_yaml.md
index 4c913a11..616fc145 100644
--- a/doc/stacker_yaml.md
+++ b/doc/stacker_yaml.md
@@ -61,6 +61,8 @@ Hub.
 `built`: `tag` is required, everything else is ignored. `built` bases this
 layer on a previously specified layer in the stacker file.
 
+`scratch`: which is an empty rootfs and can be used to host statically built binaries.
+
 ### `import`
 
 The `import` directive describes what files should be made available in