Add info on figure shortcode

Author: david-martin

content/en/docs/contribute/new-content/blogs-case-studies.md

@@ -124,6 +124,10 @@ Submissions need to be in Markdown format to be used by the [Hugo](https://gohug
 for the blog. There are [many resources available](https://gohugo.io/documentation/) on how to use
 this technology stack.
 
+For illustrations, diagrams or charts, the [figure shortcode](https://gohugo.io/content-management/shortcodes/#figure)
+can be used. For other images, we strongly encourage use of alt attributes; if an image doesn't
+need any alt attrribute, maybe it's not needed in the article at all.
+
 We recognize that this requirement makes the process more difficult for less-familiar folks to
 submit, and we're constantly looking at solutions to lower this bar. If you have ideas on how to
 lower the barrier, please volunteer to help out.