scribble/lncs: doc repair

Merge to v6.0
(cherry picked from commit 8514662b83)

pkgs/scribble-pkgs/scribble-doc/scribblings/scribble/lncs.scrbl

@@ -29,7 +29,8 @@ Similar to @racket[include-section], but incorporates the document in the
 specified module as an abstract. The document must have no title or
 sub-parts.}
 
-@defform/subs[(authors auth ...)
+@defform/subs[#:literals (author)
+              (authors auth ...)
               ([auth (author pre-content-expr ...)
                      (author #:inst str-expr pre-content-expr ...)])
               #:contracts ([pre-content-expr pre-content?]
@@ -42,6 +43,9 @@ arguments to @racket[institutes].
 }
 
 
+@defidform[author]{For use only in @racket[authors].}
+
+
 @defform[#:literals (institute)
          (institutes (institute pre-content-expr ...) ...)
          #:contracts ([pre-content-expr pre-content?])]{