[Keyboard] Add handwired BDN9-BLE (#8192)

* Add handwired BDN9-BLE

* Apply suggestions from code review

Co-Authored-By: Ryan <fauxpark@gmail.com>

* Update keyboards/handwired/bdn9_ble/rules.mk

Co-Authored-By: Ryan <fauxpark@gmail.com>

* Update keyboards/handwired/bdn9_ble/rules.mk

Co-Authored-By: Ryan <fauxpark@gmail.com>

* Update keyboards/handwired/bdn9_ble/readme.md

Co-Authored-By: James Young <18669334+noroadsleft@users.noreply.github.com>

Co-authored-by: Ryan <fauxpark@gmail.com>
Co-authored-by: James Young <18669334+noroadsleft@users.noreply.github.com>

keyboards/handwired/bdn9_ble/bdn9_ble.h

@@ -0,0 +1,37 @@
+/* Copyright 2019 Danny Nguyen <danny@keeb.io>
+ *
+ * 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/>.
+ */
+#pragma once
+
+#include "quantum.h"
+
+/* This a shortcut to help you visually see your layout.
+ *
+ * The first section contains all of the arguments representing the physical
+ * layout of the board and position of the keys.
+ *
+ * The second converts the arguments into a two-dimensional array which
+ * represents the switch matrix.
+ */
+#define LAYOUT( \
+    KA1, KA2, KA3, \
+    KB1, KB2, KB3, \
+    KC1, KC2, KC3 \
+) \
+{ \
+    { KA1, KA2, KA3 }, \
+    { KB1, KB2, KB3 }, \
+    { KC1, KC2, KC3 } \
+}