fix: doc string for all DocInfo

DocGen4/Output/Module.lean

@@ -81,6 +81,8 @@ def docInfoToHtml (module : Name) (doc : DocInfo) : HtmlM Html := do
   | DocInfo.definitionInfo i => definitionToHtml i
   | DocInfo.instanceInfo i => instanceToHtml i
   | DocInfo.classInductiveInfo i => classInductiveToHtml i
+  | i => match i.getDocString with
+    | some d => pure #[docStringToHtml d]
     | _ => pure #[]
 
   let attrs := doc.getAttrs