Add comment explaining what the matching items are for `TOO_LONG_FIRS…

…T_DOC_PARAGRAPH` lint

clippy_lints/src/doc/too_long_first_doc_paragraph.rs

@@ -21,6 +21,8 @@ pub(super) fn check(
  if first_paragraph_len <= 200
  || !matches!(
  item.kind,
+ // This is the list of items which can be documented AND are displayed on the module
+ // page. So associated items or impl blocks are not part of this list.
  ItemKind::Static(..)
  | ItemKind::Const(..)
  | ItemKind::Fn(..)