This file is a temporary file so that the directory /docs/reference/rules/rest/ will exist when the API ref docs are generated by DocGen in anyone's client.
In your client, this file will be replaced with the API ref docs when you run:
blaze run //google/firebase/service:docGen which pulls from the proto files
in the google3/google/firebase/service/ directory.
After the ref docs are officially submitted in a separate CL, this file will be automatically and permanently deleted.