Unify examples, add notes

examples/arduino-blink/platformio.ini

@@ -16,3 +16,26 @@ board = pico
 
 [env:nanorp2040connect]
 board = nanorp2040connect
+
+[env:pico_earle]
+board = pico
+; "pico" board can use both mbed and earlephilhower core, must select here
+board_build.core = earlephilhower
+
+[env:nanorp2040connect_earle]
+board = nanorp2040connect
+; "nanorp2040connect" board can use both mbed and earlephilhower core, must select here
+board_build.core = earlephilhower
+
+; earlephilhower-only boards
+[env:rpipico]
+board = rpipico
+
+[env:adafruit_feather]
+board = adafruit_feather
+
+[env:seeed_xiao_rp2040]
+board = seeed_xiao_rp2040
+
+[env:sparkfun_thingplusrp2040]
+board = sparkfun_thingplusrp2040