Add more links across docs

docs/docs/what-is-mdx.mdx

@@ -17,6 +17,7 @@ It shows how markdown, JSX, JavaScript expressions, and `import` and
 `export` statements in ESM can be used inside MDX. {/* more */}
 See [§ Getting started][start] for details on how to integrate MDX into your
 project.
+See [§ Using MDX][use] when you’re already all set up to use MDX.
 
 ## Contents
 
@@ -337,7 +338,8 @@ Which causes an error as it is misnested.
 
 ## Further reading
 
-* If you want to use MDX in your project, see [§ Getting started][start]
+* If you want to use MDX in your project, see [§ Getting started][start];
+  see [§ Using MDX][use] when you’re already all set up
 * If you’re getting errors when working with the format, see
   [§ Troubleshooting MDX][trouble]