[Keyboard] Add Frost68 keyboard (#20370)

Co-authored-by: Pablo Martínez <58857054+elpekenin@users.noreply.github.com>
Co-authored-by: Drashna Jaelre <drashna@live.com>
Co-authored-by: Joel Challis <git@zvecr.com>
Co-authored-by: jack <0x6a73@protonmail.com>

keyboards/skeletonkbd/frost68/readme.md

@@ -0,0 +1,27 @@
+# skeletonkbd/skeleton68
+
+![skeletonkbd/skeleton68](https://i.imgur.com/ZrtbBNPh.jpg)
+
+Alice layout keyboard with acrylic case.
+
+-   Keyboard Maintainer: [SkeletonKBD](https://github.com/skeletonkbd)
+-   Hardware Supported: Frost68
+-   Hardware Availability: https://github.com/skeletonkbd/Frost68
+
+Make example for this keyboard (after setting up your build environment):
+
+    make skeletonkbd/skeleton68:default
+
+Flashing example for this keyboard:
+
+    make skeletonkbd/skeleton68: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