Update hrefs in readme

README.md

@@ -22,7 +22,7 @@ If you include a future timestamp on a post, the post won't get created until th
 * **To hide a page from the sitemap XML:** add `sitemap: false` in the front matter
 * **To display a published date on a static page:** just add `date: <timestamp>` as per blog posts
 * **To display a cover image at the top of the post:** add `image: /assets/img/my-header-image.jpg` in the front matter (NB: requires complete relative path so that RSS feed generates correct link)
-* **To ensure books have a thumbnail on the [book review page](https://mojovation.co.uk/books):** add `cover: my-book-image.jpg` in the front matter
+* **To ensure books have a thumbnail on the [book review page](https://mojovation.co.uk/books):** add `cover: /assets/img/my-book-image.jpg` in the front matter
 
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