description of Middle-Colors-Twice mode

[t0mpr1c3]

The description does not quite match what AYAB does, or will do in version 1.0.0.

(1) AYAB will no longer knit white first. Instead, the most common colour is chosen as the background colour.

(2) AFAIK the sequence does not begin 2 rows white, 2 rows grey, 2 rows black, 2 rows grey, etc. Instead, it begins with only 1 row of the background colour.