Gosh. Why was there never a README in here explaining what it does
without requiring people to read C++? There was a half-assed grammar in
a comment, but it was very half-assed, so let's replace it with a
better-written one.
I'm documenting this so that neither I nor anyone else have to read C++
while rewriting the parser in Python.
See: https://git.lix.systems/lix-project/lix/issues/1196
Change-Id: Ia34ea7b02f109eb7753833e1c03d4b5d1d3c3b75
