Added SideNav component.

components/layout/SideNav.js

@@ -0,0 +1,17 @@
+import { Menu, Item } from 'react-basics';
+import Link from 'next/link';
+import styles from './SideNav.module.css';
+
+export default function SideNav({ selectedKey, items, shallow }) {
+  return (
+    <Menu items={items} selectedKey={selectedKey} className={styles.menu}>
+      {({ key, label, url }) => (
+        <Item key={key} className={styles.item}>
+          <Link href={url} shallow={shallow}>
+            {label}
+          </Link>
+        </Item>
+      )}
+    </Menu>
+  );
+}