docs: added automation step

Author: UlisesGascon

README.md

@@ -19,11 +19,16 @@ The [iojs.org](./iojs.org) directory contains the [aliases.json](./iojs.org/alia
 
 Since access to the Mailgun API key is required, only members of the @nodejs/build-infra team have the permission to push code to the `main` branch. That was done in order to minimize the possibility of mismatches between the information in this repo, and the actual email routes that are set up.
 
-### Procedure
+### Automatic Procedure
+
+There are two GitHub Actions workflows that run automatically when targeting changes to the `main` branch:
+- `ci.yml` this workflow runs the update in `dry-run` mode and reports the changes that would be made. It is triggered by any PR against the `main` branch.
+- `cd.yml` this workflow runs the update and actually applies the changes. It is triggered by any push to the `main` branch.
+### Manual Procedure
 
 The [update](./update) directory contains a node program which will read the aliases mapping file, fetch the list of mail routes from Mailgun and update the routes to make sure they match the required state. The program is run by passing it a domain name as an argument (`update/update.js iojs.org`).
 
-The Mailgun API key for the given domain is required. It can be found in the `admin_logins.md` file in the secrets repo (build/infra/), or directly via the Rackspace API. The key should be stored as a file named `iojs.org/credentials.json` in the form: `{ "api-key": "key-abc..." }` within a code tree.
+The Mailgun API key for the given domain is required. It can be found in the `admin_logins.md` file in the secrets repo (build/infra/), or directly via the Rackspace API. The key should be used as environment variable `MAILGUN_API_KEY` when running the program.
 
 The programs can be used with `--dry-run` to verify the current status and what will be changed by an update.