Refresh test credentials (#1810)

Author: Elias Kassell

test_credentials/BUILD

@@ -2,6 +2,15 @@ load("//tools/gcloud:secrets.bzl", "gcloud_secret")
 
 package(default_visibility = ["//visibility:public"])
 
+# You can update the credentials for testing by:
+# * Ensuring you have the required permissions (at time of writing, you need to request a grant).
+# * Go to the "Service Accounts" page on the "dataform-open-source" GCP project.
+# * Expand the "dataform-testing@dataform-open-source.iam.gserviceaccount.com" account.
+# * Go to the "Keys" tab, click "Add Key", and select "Create a New Key", in JSON format.
+# * Download the key, and run the `dataform init-creds` CLI command on the JSON.
+# * Copy the resulting `.df-credentials` file to here as `bigquery.json`.
+# * Run the "scripts/create_secret" script.
+# TODO(ekrekr): make this process easier, as keys invalidate themselves fairly frequently now.
 gcloud_secret(
     name = "bigquery.json",
     testonly = 1,