docs(codes): Add (key) codes documentation

Create codes documentation for standardized keys.

Closes #218.  Fixes #308.  Ref #21.

docs/src/data/hid-usage-pages.js

@@ -0,0 +1,9 @@
+/*
+ * Copyright (c) 2020 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: CC-BY-NC-SA-4.0
+ */
+
+export const genericDesktop = 0x01;
+export const key = 0x07;
+export const consumer = 0x0c;