Document changes in release process

Author: bogsi17

README.md

@@ -89,6 +89,11 @@ candidate. Now it's time to deploy. Start with a deploy to `training` or
 `preview` to ensure the tagged version is correct. Once that's done you can
 deploy to production.
 
+Use the `deploy.yml` workflow to run the deployments. For the production deployment,
+it's important to start the workflow from the `main` branch and specify the tag to deploy
+as input. This is because only workflows from the `main` branch can authenticate with the
+production AWS account.
+
 #### When `release` and `main` have diverged
 
 There are cases when `release` won't be fast-forwardable to the release