I was able to find an answer on stackoverflow. It doesn't seem to be documented on googles website anywhere:
You need to download the SDK reference documentation:
Navigate to the directory where you want to install the docs in the
command line. If you used ~/google-cloud-ml to download the samples as recommended in the setup guide, it's a good place.
Copy the documentation archive to your chosen directory using gsutil:
gsutil cp gs://cloud-ml/sdk/cloudml-docs.latest.tar.gz .
Unpack the archive:
tar -xf cloudml-docs.latest.tar.gz
This creates a docs directory inside the directory that you chose. The documentation is essentially a local website: open docs/index.html in your browser to open it at its root. You can find the transform references in there.
(This information is now in the setup guide as well. It's the final step under LOCAL: MAC/LINUX)
https://stackoverflow.com/a/40519472/6283150