Update chips/index.md

[cmfcmf]

@freepdk made a comment here: 1667faf#r40725763

MCU390 is supported by easy pdk prog, I have some at hand.

Looks like MCU39X is a customized PADAUK version from this company:
http://www.zhienchina.com/products/1556.html
The chip comes with SDK for touch sensing: http://www.zhienchina.com/Upfiles/down/%E8%8A%AF%E8%BE%BE%E8%A7%A6%E6%91%B8MCU39x.rar

They also have the XDM varaints (see above) with integrated eeprom (looks like a multichip package - 2 ics in one package):
http://www.zhienchina.com/product/MCU.html