fix lists docs regression (#16981)

lib/pure/collections/lists.nim

@@ -13,15 +13,11 @@
 ## * `singly linked rings <#SinglyLinkedRing>`_ (circular lists)
 ## * `doubly linked rings <#DoublyLinkedRing>`_ (circular lists)
 ##
-##
-## Basic Usage
-## ===========
-##
+## # Basic Usage
 ## Because it makes no sense to do otherwise, the `next` and `prev` pointers
 ## are not hidden from you and can be manipulated directly for efficiency.
-##
-## Lists
-## -----
+
+## ## Lists
 runnableExamples:
   var
     l = initDoublyLinkedList[int]()
@@ -40,8 +36,7 @@ runnableExamples:
   assert c.prev == nil
   assert b.next == nil
 
-## Rings
-## -----
+## ## Rings
 runnableExamples:
   var
     l = initSinglyLinkedRing[int]()
@@ -59,9 +54,7 @@ runnableExamples:
   assert b.next == c
   assert c.next.next.next == c
 
-## See also
-## ========
-##
+## # See also
 ## * `deques module <deques.html>`_ for double-ended queues
 ## * `sharedlist module <sharedlist.html>`_ for shared singly-linked lists