Insert commas at randomly selected words. This function modifies values
inside <code>words</code> array
@param {Array} words
function insertCommas(words) {
	if (words.length < 2) {
		return words;
	}

	words = words.slice();
	const len = words.length;
	const hasComma = /,$/;
	let totalCommas = 0;

	if (len > 3 && len <= 6) {
		totalCommas = rand(0, 1);
	} else if (len > 6 && len <= 12) {
		totalCommas = rand(0, 2);
	} else {
		totalCommas = rand(1, 4);
	}

	for (let i = 0, pos, word; i < totalCommas; i++) {
		pos = rand(0, len - 2);
		if (!hasComma.test(words[pos])) {
			words[pos] += ',';
		}
	}

	return words;
}