Update .gitignore

Ignoring S340 SD specific license-bound files

Author: orrmany

.gitignore

@@ -20,3 +20,6 @@
 # Ignore local overrides of platform.txt and boards.txt,
 /boards.local.txt
 /platform.local.txt
+bootloader/feather_nrf52840_express/feather_nrf52840_express_bootloader-0.3.0_s340_6.1.1.hex
+bootloader/feather_nrf52840_express/feather_nrf52840_express_bootloader-0.3.0_s340_6.1.1.zip
+cores/nRF5/nordic/softdevice/s340_nrf52_6.1.1_API/*