[Feature Request] Add RunKit template for npm.runkit.com integration

[Olian04]

Is your feature request related to a problem? Please describe.
NPM provides a "Try on RunKit" button, however the default template used by RunKit doesn't show off any features of better-logging.

var betterLogging = require("better-logging")

Describe the solution you'd like

As described in this article on RunKit+NPM we can define our own RunKit template by adding a property to package.json.

// package.json
{
  "name": "better-logging",
  "version": "4.5.0",
   "runkitExampleFilename": "./demo/runkit.template.js"
  // ...
}

// demo/runkit.template.js
require('better-logging')(console);

console.log('This will print fine!');
console.info('So will this!');
console.warn('And this!');
console.error('This one as well!');
console.debug('This won\'t! To low log level');

// Enable debug output
console.logLevel = 4;

console.log('This will print fine, AGAIN!');
console.info('So will this, AGAIN!');
console.warn('And this, AGAIN!');
console.error('This one as well, AGAIN!');
console.debug('Now this will print!');

Known issues

• For some reason console.debug doesn't work at all (only on RunKit).
• RunKit defaults to Node version 10.x, which better-logging doesn't support.

Additional context

• Runkit Docs: https://runkit.com/docs/resources
• Supported engine versions: [Feature Request] Add engines property to package.json #56

Other
If this issues get resolved, then we could add a "Try on RunKit" badge to the readme.