Add missed file

Author: makermelissa

_board/warmbit_bluepixel.md

@@ -4,7 +4,7 @@ board_id: "warmbit_bluepixel"
 title: "Warmbit BluePixel Download"
 name: "Warmbit BluePixel"
 manufacturer: "Warmbit"
-board_url: ""
+board_url:
 board_image: "unknown.jpg"
 date_added: 2021-9-3
 family: nrf52840