add 816

Author: ladyada

build_platform.py

@@ -115,6 +115,7 @@
     "feather_rp2040_tinyusb" : "rp2040:rp2040:adafruit_feather:flash=8388608_0,freq=125,dbgport=Disabled,dbglvl=None,usbstack=tinyusb",
     # Attiny8xy (SpenceKonde)
     "attiny817" : "megaTinyCore:megaavr:atxy7:chip=817",
+    "attiny816" : "megaTinyCore:megaavr:atxy6:chip=816",
     # groupings
     "main_platforms" : ("uno", "leonardo", "mega2560", "zero",
                         "esp8266", "esp32", "metro_m4", "trinket_m0"),