Add documentation for external image usage

layouts/_default/single.html

@@ -1,10 +1,5 @@
 {{ define "main" }}
 {{ .Scratch.Set "scope" "single" }}
-<style>
-  .max-w-fit, .max-w-prose {
-    max-width: {{.Params.maxWidth}}ch
-}
-</style>
 
 <article>
   {{ if .Params.showHero | default (.Site.Params.article.showHero | default false) }}