doc: clarify process.title inconsistencies

Many users assume the act of assigning a value to process.title will update the name of their process in apps like macOS Activity Monitor or Windows Services Manager. This has worked in the past, but fails in some versions of Node.js. Ultimately developers are left confused, especially when it works in one version of Node.js and not another. Given the recurring nature and complexity of the underlying issue, it does not seem like a resolvable problem. This note clarifies the source of the problem and sets developer expectations.

Fixes: https://github.com/nodejs/node/issues/34280

Checklist

• documentation is changed or added
• commit message follows commit guidelines