Request: Improved comments/docs

[Dan Simmons-Ritchie]

The folks in Texas would be super appreciative if some docstrings could be added to a number of the funcs in this repo (eg. getSpecialNav) 🙏

I'm just finding it a bit difficult to understand exactly why certain args are required in certain funcs. Docstrings would be super helpful.

I'd suggest JSDoc style. Eg.:

 * Takes 2 numbers and returns their sum.
 * @param   {number} a the first number
 * @param   {number} b the second number
 *
 * @returns {number} the sum of a and b
 */
function addNumbers(a, b) {
  return a + b;
}