docs(codes): Add (key) codes documentation

Create codes documentation for standardized keys.

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

docs/src/components/codes/LinkIcon.jsx

@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) 2020 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: CC-BY-NC-SA-4.0
+ */
+
+import React from "react";
+import { FontAwesomeIcon } from "@fortawesome/react-fontawesome";
+import { faExternalLinkAlt } from "@fortawesome/free-solid-svg-icons";
+export default function LinkIcon() {
+  return <FontAwesomeIcon className="icon" icon={faExternalLinkAlt} />;
+}
+
+LinkIcon.propTypes = {};