Merge pull request #2345 from bmuenzenmeyer/docker-image-flow

Documents docker image flow

Author: MikeMcC399

CONTRIBUTING.md

@@ -29,6 +29,15 @@ New **npm** releases are not tracked. We simply use the npm version bundled in t
 
 **[Yarn v1 Classic](https://classic.yarnpkg.com/)** is no longer maintained upstream, and will be removed starting with the Node 26 images.
 
+### Image Creation Automation
+
+- Every 15 minutes, the [workflow](https://github.com/nodejs/docker-node/blob/main/.github/workflows/automatic-updates.yml) within the [nodejs/docker-node](https://github.com/nodejs/docker-node) repo [checks](https://github.com/nodejs/docker-node/blob/main/build-automation.mjs) for new versions of Node.js [published to the website's `index.json` file](https://nodejs.org/download/release/index.json).
+  - If found, it also checks for an [unofficial musl/Alpine build](https://unofficial-builds.nodejs.org/download/release/index.json).
+  - If found, the [update script](https://github.com/nodejs/docker-node/blob/main/update.sh) runs
+  - The workflow opens a pull request either automatically via [nodejs-github-bot](https://github.com/nodejs-github-bot) or in some cases manually, such as when there is a new major release.
+- Another [workflow](https://github.com/nodejs/docker-node/blob/main/.github/workflows/official-pr.yml) detects the merger of these pull requests and opens a pull request to [docker-library/official-images](https://github.com/docker-library/official-images).
+- The official images are built and published according to [docker's process](https://github.com/docker-library/faq#an-images-source-changed-in-git-now-what), resulting in the new images being available on [Docker Hub](https://hub.docker.com/_/node).
+
 ### Submitting a PR for a version update
 
 If you'd like to help us by submitting a PR for a version update, please do the following: