update README to include apigee directory

docker/README.md

diff --git a/docker/README.md b/docker/README.md
index ddd12f3..76cd718 100644
--- a/docker/README.md
+++ b/docker/README.md
@@ -1,3 +1,4 @@
 - copy this Dockerfile file to the mixer repo root
 - cp the mixs and mixc binary to mixer repo root (since bazel builds binary in tmp directory outside the mixer root, this step is needed)
+- create testdata/apigee
 - docker build