Add doc comment

Author: brianrourkeboll

src/FSharp.Formatting.Common/HtmlModel.fs

@@ -751,5 +751,6 @@ module internal Html =
     let iconifyIcon (props: HtmlProperties list) =
         HtmlElement.CustomElement("iconify-icon", props, [])
 
+    /// Toggle button for API doc details.
     let fsdocsDetailsToggle (props: HtmlProperties list) =
         HtmlElement.CustomElement("fsdocs-details-toggle", props, [])