README: upgrade MacOS stability and note

[cole-h]

Removing users and/or groups may fail if there is no user logged in graphically. Aside from that, it should work.

Description

#33 is closed and removal of users and groups has been re-enabled.

Checklist

• Formatted with cargo fmt
• Built with nix build
• Ran flake checks with nix flake check
• Added or updated relevant tests (leave unchecked if not applicable)
• Added or updated relevant documentation (leave unchecked if not applicable)
• Linked to related issues (leave unchecked if not applicable)

Validating with install.determinate.systems

If a maintainer has added the upload to s3 label to this PR, it will become available for installation via install.determinate.systems:

curl --proto '=https' --tlsv1.2 -sSf -L https://install.determinate.systems/nix/pr/$PR_NUMBER | sh -s -- install

[Hoverbear]

Good catch!!! Thanks!