Add config for Atreus based on Adafruit Feather BLE (#9140)

Co-authored-by: Joel Challis <git@zvecr.com>
Co-authored-by: Ryan <fauxpark@gmail.com>
Co-authored-by: Drashna Jaelre <drashna@live.com>
Co-authored-by: Erovia <Erovia@users.noreply.github.com>

keyboards/atreus/feather/rules.mk

@@ -0,0 +1,21 @@
+# MCU name
+MCU = atmega32u4
+
+# Processor frequency
+F_CPU = 8000000
+
+# Bootloader selection
+#   Teensy       halfkay
+#   Pro Micro    caterina
+#   Atmel DFU    atmel-dfu
+#   LUFA DFU     lufa-dfu
+#   QMK DFU      qmk-dfu
+#   ATmega32A    bootloadHID
+#   ATmega328P   USBasp
+BOOTLOADER = caterina
+
+# Build Options
+#   change yes to no to disable
+#
+BLUETOOTH = AdafruitBLE
+CONSOLE_ENABLE = no