[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/rabbit68.c

@@ -0,0 +1,51 @@
+/* Copyright 2019 Kai Eckert
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include "rabbit68.h"
+
+// Optional override functions below.
+// You can leave any or all of these undefined.
+// These are only required if you want to perform custom actions.
+
+/*
+
+void matrix_init_kb(void) {
+  // put your keyboard start-up code here
+  // runs once when the firmware starts up
+
+  matrix_init_user();
+}
+
+void matrix_scan_kb(void) {
+  // put your looping keyboard code here
+  // runs every cycle (a lot)
+
+  matrix_scan_user();
+}
+
+bool process_record_kb(uint16_t keycode, keyrecord_t *record) {
+  // put your per-action keyboard code here
+  // runs for every action, just before processing by the firmware
+
+  return process_record_user(keycode, record);
+}
+
+void led_set_kb(uint8_t usb_led) {
+  // put your keyboard LED indicator (ex: Caps Lock LED) toggling code here
+
+  led_set_user(usb_led);
+}
+
+*/