Document 4.2" V2 driver.

DRIVERS.md

@@ -1395,6 +1395,7 @@ image:
 There are two drivers for the V1 display:
  1. `pico_epaper_42.py` 1-bit black/white driver supports partial updates.
  2. `pico_epaper_42_gs.py` 2-bit greyscale driver. No partial updates.
+
  Currently the V2 display has only a 1-bit driver, contributed by Michael
  Surdouski. It supports partial updates.
  1. `pico_epaper_42_v2.py`