site: add image dimensions for approach top image

Author: XhmikosR

site/src/approach.njk

@@ -17,7 +17,7 @@ sections:
 
 ## How it works
 
-![](/assets/images/graphs/what-is-prefetch-svgomg.svg)
+<img class="article-image" src="/assets/images/graphs/what-is-prefetch-svgomg.svg" height="932" width="535" alt="Image shows how prefetching improves page load speed by fetching resources in advance">
 
 Quicklink attempts to make navigations to subsequent pages load faster. It: