[Keyboard] Add pico as a new keyboard (#7419)

* Add keyboards/ pico as a new keyboad.

* Add keyboards/pico rev1.

* Add keyboards/pico keymaps/default.

* Add keyboards/pico keymaps/jis.

* Remove unneeded code of rules.mk.

* Revert rules.mk and remove some comments.

keyboards/pico/pico.h

@@ -0,0 +1,23 @@
+/* Copyright 2019 Kumao Kobo <kumaokobo@gmail.com>
+ *
+ * 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
+
+#ifdef KEYBOARD_pico_rev1
+    #include "rev1.h"
+#endif
+
+#include "quantum.h"