[www] Add PostLink component example to docs/adding-a-list-of-markdown-blog-posts/

docs/docs/adding-a-list-of-markdown-blog-posts.md

@@ -39,7 +39,7 @@ export default IndexPage;
 
 ### Creating the GraphQL query
 
-The only thing left to do is to provide the data to your component with a GraphQL query.
+Second, you need to provide the data to your component with a GraphQL query. Let's add it, so that `index.js` looks like this:
 
 ```js
 import React from "react";
@@ -74,4 +74,23 @@ export const pageQuery = graphql`
 `;
 ```
 
-This should get you a page with your posts sorted by descending date. You can further customise the `frontmatter` and the page component to get desired effects!
+### Creating the `PostLink` component
+
+The only thing left to do is to add the `PostLink` component. Create a new file `post-link.js` in `src/components/` and add the following:
+
+```js
+import React from "react";
+import Link from "gatsby-link";
+
+const PostLink = ({ post }) => (
+  <div>
+    <Link to={post.frontmatter.path}>
+      {post.frontmatter.title} ({post.frontmatter.date})
+    </Link>
+  </div>
+);
+
+export default PostLink;
+```
+
+This should get you a page with your posts sorted by descending date. You can further customise the `frontmatter` and the page and `PostLink` components to get desired effects!