Add Arduino Nano 33 BLE as a supported board

changes are needed in the following files:
flavours/zephyr/conf-notes.txt
flavours/zephyr/local.conf.sample

Signed-off-by: Nagesh Shamnur <nagesh.shamnur@huawei.com>

flavours/zephyr/conf-notes.txt

@@ -9,6 +9,7 @@ Supported machines (first is the default):
 - 96b-nitrogen (96Boards Nitrogen)
 - 96b-avenger96 (96Boards Avenger96)
 - nrf52840dk-nrf52840 (Nordic Semiconductor nRF 52840 Development Kit)
+- arduino-nano-33-ble (Arduino Nano 33 BLE and Arduino Nano 33 BLE Sense)
 
 MACHINE variable can be set up in conf/local.conf file under build directory
 or via command line, e.g.:

flavours/zephyr/local.conf.sample

@@ -29,6 +29,7 @@
 #MACHINE ?= "96b-nitrogen"
 #MACHINE ?= "96b-avenger96"
 #MACHINE ?= "nrf52840dk-nrf52840"
+#MACHINE ?= "arduino-nano-33-ble"
 #
 # This sets the default machine to be qemu-x86 if no other machine is selected:
 MACHINE ??= "qemu-x86"