Add note to README about where to find `.env.production` values

README.md

@@ -54,6 +54,9 @@ This project stores HTTP Basic Auth credentials and Marketo API keys in the
 environment variables, using [Dotenv]. The default values should be overridden
 in a `.env.production` file for deployment.
 
+The required values are in the [marketo-tools secrets](https://gitlab.1password.com/vaults/medb67sd6uwuzzv66nobz2hjxq/allitems/c7f6rvguqfal5ep4xgol5vjsfa)
+login in the **DevOps** vault in 1Password.
+
 ## License
 
 Copyright © 2015 GitLab, Inc. It is free software, and may be redistributed