docs: describe manual PR image creation

CONTRIBUTING.md

@@ -41,17 +41,29 @@ from templates starting with the Node 26 images.
 - 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
+### Image Creation Manually
 
-If you'd like to help us by submitting a PR for a version update, please do the following:
+Image updates for existing Node.js release lines are created automatically as described above.
+If there is a problem with the automated process, it may be necessary to create an update PR manually.
+If you believe there is a need for a manual PR, and you are not a member of the
+[Docker Maintainers](./README.md#docker-maintainers) or
+[Collaborators](./README.md#collaborators) team of this repo,
+please first open an issue to describe the update problem
+and your suggestion to resolve it.
+
+To set up a version update PR, follow these instructions:
 
 1. [Fork this project.](https://docs.github.com/en/get-started/quickstart/fork-a-repo)
 1. [Clone the forked repository.](https://docs.github.com/en/github/creating-cloning-and-archiving-repositories/cloning-a-repository)
 1. Create a branch for the update PR. For example, `git checkout main; git checkout -b version-update`.
-1. Run `./update.sh`. You can see additional options by using accessing the built-in help documentation with `./update.sh -h`. This script will automatically update the appropriate files with the latest versions and checksums.
+1. Run `./update.sh`. You can see additional options by using the built-in help documentation with `./update.sh -h`. This script will automatically update the appropriate files with the latest versions and checksums.
 1. Commit the modified files to the `version-update` branch and push the branch to your fork.
 1. [Create a PR to merge the branch from your fork into this project's default branch.](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request-from-a-fork).
 
+When a new Node.js release line is expected, additional preparation is necessary, including updates to the
+[versions.json](./versions.json) file and creation of a major version directory, populated with generated files.
+This task is undertaken by members of the repo team above.
+
 ## Adding dependencies to the base images
 
 NodeJS is a big ecosystem with a variety of different use cases. The docker images for node are designed to provide the minimum for running core node.  Additional dependencies (including dependencies for npm or yarn such as git) will not be included in these base images and will need to be included in descendent image.