[Keyboard] Add Rabbit68 Keyboard w/ default,kaiec keymaps. (#6676)

* Add Rabbit68 Keyboard w/ default,kaiec keymaps.

* Requested changes by @fauxpark

* Change flash command, as suggested by @drashna

* Update keyboards/rabbit/rabbit68/readme.md

Co-Authored-By: Drashna Jaelre <drashna@live.com>

* Add link to Github repo 

As I per suggestion changed the link above to an image, I added now the link to the project page to the Open Source text, where it actually makes the most sense.

keyboards/rabbit/rabbit68/rules.mk

@@ -0,0 +1,33 @@
+# MCU name
+MCU = atmega32u4
+
+
+# Bootloader selection
+#   Teensy       halfkay
+#   Pro Micro    caterina
+#   Atmel DFU    atmel-dfu
+#   LUFA DFU     lufa-dfu
+#   QMK DFU      qmk-dfu
+#   atmega32a    bootloadHID
+BOOTLOADER = halfkay
+
+# Build Options
+#   change yes to no to disable
+#
+BOOTMAGIC_ENABLE = no      # Virtual DIP switch configuration(+1000)
+MOUSEKEY_ENABLE = no       # Mouse keys(+4700)
+EXTRAKEY_ENABLE = yes       # Audio control and System control(+450)
+CONSOLE_ENABLE = yes        # Console for debug(+400)
+COMMAND_ENABLE = yes        # Commands for debug and configuration
+# Do not enable SLEEP_LED_ENABLE. it uses the same timer as BACKLIGHT_ENABLE
+SLEEP_LED_ENABLE = no       # Breathing sleep LED during USB suspend
+# if this doesn't work, see here: https://github.com/tmk/tmk_keyboard/wiki/FAQ#nkro-doesnt-work
+NKRO_ENABLE = no            # USB Nkey Rollover
+BACKLIGHT_ENABLE = no       # Enable keyboard backlight functionality
+RGBLIGHT_ENABLE = no        # Enable keyboard RGB underglow
+MIDI_ENABLE = no            # MIDI support (+2400 to 4200, depending on config)
+UNICODE_ENABLE = no         # Unicode
+BLUETOOTH_ENABLE = no       # Enable Bluetooth with the Adafruit EZ-Key HID
+AUDIO_ENABLE = no           # Audio output on port C6
+FAUXCLICKY_ENABLE = no      # Use buzzer to emulate clicky switches
+HD44780_ENABLE = no 		# Enable support for HD44780 based LCDs (+400)