Add "Setting up GitHub Actions auto-deployment" instructions

website/README.md

@@ -8,7 +8,7 @@ This website is built using [Docusaurus 2](https://docusaurus.io/), a modern sta
 $ npm install
 ```
 
-### Local Development
+### Local development
 
 ```
 $ npm start
@@ -39,3 +39,15 @@ $ GIT_USER=<Your GitHub username> npm run deploy
 ```
 
 If you are using GitHub pages for hosting, this command is a convenient way to build the website and push to the `gh-pages` branch.
+
+### Setting up GitHub Actions auto-deployment
+
+The [deployment workflow](../.github/workflows/deploy-website.yaml) is configured to deploy to `carbon-language.github.io` using [deploy keys](https://docs.github.com/en/developers/overview/managing-deploy-keys).
+(Personal access tokens can also be used via [`personal_token`](https://github.com/peaceiris/actions-gh-pages#%EF%B8%8F-deploy-to-external-repository-external_repository).)
+
+To configure the required deploy keys:
+
+1. Create a new SSH key pair according to the [GitHub docs](https://docs.github.com/en/authentication/connecting-to-github-with-ssh/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent#generating-a-new-ssh-key).
+2. Add the private key to the "Repository secrets" section of repository which runs the workflow, name it `ACTIONS_DEPLOY_KEY`.
+3. Add the public key to the "Deploy keys" section of the target deployment repository and enable "Allow write access".
+4. The next time the GitHub Actions workflow runs, it will use these keys to deploy the website.