Write a tutorial to complement the relatively austere "Documentation" section in the README

[amn]

Admittedly, API reference is one thing but a guide, or a tutorial is another, rightfully complementary, and no great crime to be offering. On the contrary -- in the case of this austerely documented parser -- yes, even docstrings can be a barrier to entry.

So here's to penning up a tutorial (and then look into whether more can be added with Github's own "Discussions" feature, towards the same goal of reducing barrier to entry).