[Keyboard] Add Guide68 (#19264)

Co-authored-by: jack <0x6a73@protonmail.com>

keyboards/salicylic_acid3/guide68/readme.md

@@ -0,0 +1,27 @@
+# guide68
+
+![guide68](https://i.imgur.com/u1HeHb9h.jpg)
+
+This is 68 keys Row-staggered Split keyboard.
+
+* Keyboard Maintainer: [Salicylic-acid3](https://github.com/Salicylic-acid3)
+* Hardware Supported: guide68 PCB, Pro Micro
+* Hardware Availability: [PCB & Case Data](https://github.com/Salicylic-acid3/PCB_Data)
+
+Make example for this keyboard (after setting up your build environment):
+
+    make salicylic_acid3/guide68:default
+
+Flashing example for this keyboard:
+
+    make salicylic_acid3/guide68: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