docs(readme): update minimum Node.js version requirement from v16 to v18 #119

Bug

The root README.md lists the minimum Node.js requirement as:

Node.js (v16 or higher)

Node.js v16 reached end-of-life in September 2023 and is no longer maintained. The current LTS versions are v18 and v20.

Proposed Fix

Update the requirement to:

Node.js (v18 or higher)

I'd be happy to open a PR for this fix.