diff --git a/README.md b/README.md
index 0d4cafc..75c9e3e 100644
--- a/README.md
+++ b/README.md
@@ -69,4 +69,12 @@
 
 [Debian multiarch names](https://wiki.debian.org/Multiarch/Tuples)
 
-You can add any values in `docker_build_options` object, all these values passed to docker on building
\ No newline at end of file
+You can add any values in `docker.build_options` object, all these values passed to docker on building
+
+`ppa.install_instructions` will be replaced to corresponding `install_instructions` array, or you can set array of strings directly:
+
+```
+      "ppa": {
+        "install_instructions": ["line1", "line2"]
+      }
+```