[Keyboard] add itstleo40 PCB (#21536)

Co-authored-by: jack <0x6a73@protonmail.com>
Co-authored-by: Drashna Jaelre <drashna@live.com>

keyboards/itstleo/itstleo40/readme.md

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+# itstleo/itstleo40
+
+![itstleo/itstleo40](https://i.imgur.com/snNWZPmh.jpeg)
+
+* ItsTLeo first pcb using planck mit community layout, powered by QMK with VIA supported
+
+* Keyboard Maintainer: [ItsTLeo](https://github.com/ItsTLeo)
+* Hardware Supported: Powered with RP2040
+
+Make example for this keyboard (after setting up your build environment):
+
+    make itstleo/itstleo40:default
+
+Flashing example for this keyboard:
+
+    make itstleo/itstleo40: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 `QK_BOOT` if it is available