[Keymap] Add andrebrait layout for GMMK Pro (#13932)

keyboards/gmmk/pro/ansi/keymaps/andrebrait/readme.md

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+# andrebrait's GMMK Pro layout
+
+This is pretty much the stock layout with a few things moved around.
+It basically reflects my needs for both Delete and Insert being readily available for coding, as well as a full Home/PgUp/PgDwn/End column.
+
+The differences are as follows:
+
+- Short DEBOUNCE time (5 ms)
+- Per-key debounce algorithm (sym_defer_pk)
+- RGB turns off after 20 minutes of inactivity
+- RGB turns off when USB is suspended
+- Layer 0:
+  - Print Screen (default) -> Delete
+  - Delete (default) -> Home
+- Layer 1 (accessed by pressing Fn):
+  - Fn + Delete -> Insert
+  - Fn + Home -> Print Screen
+
+This keymap also includes CAPS LOCK ON indicator.\
+All left and right side LEDs, and the Caps key LED will turn solid red while CAPS LOCK is ON.
+
+No other changes have been made. \
+The other keys on each layer have been kept intact.