Update sidebar.mdx

Author: LB

packages/docs/src/sidebar.mdx

@@ -1,5 +1,4 @@
-- Getting Started
-  - [Getting Started](/getting-started)
+- [Getting Started](/getting-started)
   - [Getting Started with Gatsby](/getting-started/gatsby)
 - [Theming](/theming)
 - [The `sx` Prop](/sx-prop)