docs: misleading CONTRIBUTING invitation to update versions

[MikeMcC399]

Problem

The CONTRIBUTING document, section Submitting a PR for a version update implies that there is a need for community help in updating to new versions.

The instructions refer to running ./update.sh.

This seems to be in conflict with the GitHub Actions workflow automatic-updates.yml that runs every 15 minutes and automatically updates.

Solution

Perhaps the section Submitting a PR for a version update should be removed? It should at least be put into context with the actions of the automatic-updates.yml workflow.

[MikeMcC399]

This is also related to #2363 since the automated update is gated on the prerequisites for all Docker variants being available. It is currently blocked from completion if the musl unofficial builds required for the Alpine images are not available for the related Node.js release on https://unofficial-builds.nodejs.org/download/release/.

[PeterDaveHello]

Indeed, we hope to accomplish this as much as possible through automated processes. However, given that recent Alpine builds have often been delayed, manual updates are also an option to consider — it’s just that how to properly describe this part may require some thought.