Add a warning when a common mistake is detected: @module tag required

[75lb]

Print a warning and a link to the wiki when the most common user mistake is detected: @module tag required, documented here.

Warning output to look something like this:

Module tag required in this file: /Users/lloyd/Documents/example-src.js
See the wiki for an explanation: https://github.com/jsdoc2md/jsdoc-to-markdown/wiki/How-to-document-an-ES2015-module-(single-default-export)