mcrown crkbd new keymap (#12092)

Co-authored-by: Erovia <Erovia@users.noreply.github.com>

keyboards/crkbd/keymaps/mcrown/readme.md

@@ -0,0 +1,13 @@
+![the-frey-layout](https://raw.githubusercontent.com/MarioCorona/mcrown_pics/main/mcrown_layout.png)
+
+# Keyboard layout by MCrown
+
+This is all four layers:
+
+- The top indicates the RAISE layer
+- The middle indicates the DEFAULT layer
+- The bottom indicates the LOWER layer
+- Green indicated ADJUST layer
+
+All the keys respond as you'd expect to the 'shift' key - i.e. on a UK/GB keyboard, `/` becomes `?` and so on.
+