Add notice for newer Node.js versions

[1j01]

Re: #1031 (comment) and other issues like #1027 and #1037 and #1010 and #1013 and #1024

This is my suggested course of action to help googlers (there're lots of links pointing to node-inspector as a definitive solution) and especially people who've used this project before but have since updated Node.js:

• Update package.json engines field to reflect the latest supported version of node (this can of course be upated later if support is ever added for later Node.js versions)
• Add a (conditional*) message to the output of the install script to let users know what they can do to debug in later Node.js versions, namely node --inspect or node --inspect-brk and opening chrome://inspect in Chrome (which automagically detects it (on the default ports)) (or using other options listed on the docs: https://nodejs.org/en/docs/guides/debugging-getting-started/)
• Add a notice to the README

*Such a condition could look like this:

const semver = require('semver');
const {engines} = require('./package.json');
const nodeVersionRange = engines.node;
if (!semver.satisfies(process.version, nodeVersionRange)) {
  console.error(`node-inspector requires a Node.js version ${nodeVersionRange}; this range is not satisfied by ${process.version}. Later versions of Node.js have flags --inspect and --inspect-brk which can be used together with inspector clients like chrome://inspect in Chrome, or others as listed in the docs: https://nodejs.org/en/docs/guides/debugging-getting-started/`);
  process.exitCode = 1;
  return;
}