[Keyboard] Add keyboard "Spreadwriter" (#17031)

Co-authored-by: Joel Challis <git@zvecr.com>
Co-authored-by: Drashna Jaelre <drashna@live.com>

keyboards/takashicompany/spreadwriter/readme.md

@@ -0,0 +1,35 @@
+# takashicompany/spreadwriter
+
+![takashicompany/spreadwriter](https://i.imgur.com/mMAzyvUh.jpg)
+
+"Spreadwriter" はGL516ケースに対応した50%キーボードです。  
+放射状のキーレイアウトは、手を自然な形で置くことができ、楽な姿勢での打鍵を可能にしています。  
+
+LEDを用いたキーの照明や、ロータリーエンコーダの搭載も可能です。
+---
+"Spreadwriter" is a 50% keyboard for the GL516 case.
+The radial key layout allows for a natural hand placement and comfortable typing posture.
+
+LED-based key illumination and a rotary encoder are also available.
+
+* Keyboard Maintainer: [takashicompany](https://github.com/takashicompany)
+* Hardware Supported: Spreadwriter PCB, Pro Micro
+* Hardware Availability: https://github.com/takashicompany/spreadwriter
+
+Make example for this keyboard (after setting up your build environment):
+
+    make takashicompany/spreadwriter:default
+
+Flashing example for this keyboard:
+
+    make takashicompany/spreadwriter:default:flash
+
+See the [build environment setup](https://docs.qmk.fm/#/getting_started_build_tools) and the [make instructions](https://docs.qmk.fm/#/getting_started_make_guide) for more information. Brand new to QMK? Start with our [Complete Newbs Guide](https://docs.qmk.fm/#/newbs).
+
+## Bootloader
+
+Enter the bootloader in 3 ways:
+
+* **Bootmagic reset**: Hold down the key at (0,0) in the matrix (usually the top left key or Escape) and plug in the keyboard
+* **Physical reset button**: Briefly press the button on the back of the PCB - some may have pads you must short instead
+* **Keycode in layout**: Press the key mapped to `RESET` if it is available