docs: update Alpine size descriptions

[MikeMcC399]

• closes Review description of image sizes in README #2432

Description

Convert the size-related information in the README node:alpine section to fact-based, verifiable statements.

Remove opinionated recommendation statements.

Motivation and Context

The README node:alpine section has a high emphasis on image size as the basis for selection. It quotes the size of the original base image without comparing the size of the images after Node.js has been added.

It unconditionally recommends node:alpine on the basis of size. This is without regard for the currently higher Tier 1 / 2 status of Debian images. This may lead users to chose Alpine images where node:slim Docker images may be a better fit.

Testing Details

N/A - documentation change only

Types of changes

• Documentation
• Version change (Update, remove or add more Node.js versions)
• Variant change (Update, remove or add more variants, or versions of variants)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Other (none of the above)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING.md document.
• All new and existing tests passed.

[MikeMcC399]

Preview

https://github.com/MikeMcC399/docker-node/blob/alpine-size-description/README.md#nodealpine

[MikeMcC399]

A next step would be to update the musl section from a technical (and then supportability) standpoint. See #2497