The plan9/386 builder uses the binary package.
diff --git a/Plan9.md b/Plan9.md
index ded3967..a773900 100644
--- a/Plan9.md
+++ b/Plan9.md
@@ -103,6 +103,8 @@
 
 A [binary package](https://storage.googleapis.com/go-builder-data/gobootstrap-plan9-386.tar.gz) for plan9/386 is available.
 
+This binary package is used to bootstrap Go on the plan9/386 builder.
+
 ```
 cd /tmp
 hget -o gobootstrap-plan9-386.tar.gz https://storage.googleapis.com/go-builder-data/gobootstrap-plan9-386.tar.gz