docs: update Alpine musl descriptions

[MikeMcC399]

Description

Convert the musl-related information in the README node:alpine section to a shorter form.

Remove the opinion that "this variant is a very safe choice".

Motivation and Context

The README node:alpine section refers to the use of musl instead of glibc and suggests that it is a safe choice.

This is in contrast to:

• known compatibility issues for applications written and compiled for glibc (Debian, and related distros such as Ubuntu & Fedora) that do not run under musl
• Experimental support type category for musl on x64 only (see Node.js BUILDING > Platform list), compared to wide support by Node.js for glibc on multiple architectures as Tier 1 / 2 support type

The original text was posted 10 years ago and includes a level of detail that is not necessary for selection or use of node:alpine Docker images.

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]

Leaving in draft, pending PR #2496

I will later rebase to make reviewing the complete text more meaningful so that it shows a final version rather than a snippet of changes.