clarified options: LLNCS works with LuaLaTeX and Isabelle sections, although Springer might not like it;

--- a/src/Doc/Demo_LLNCS/ROOT	Sat Nov 05 09:57:51 2022 +0100
+++ b/src/Doc/Demo_LLNCS/ROOT	Sat Nov 05 12:12:33 2022 +0100
@@ -1,8 +1,7 @@
 chapter Doc
 
 session Demo_LLNCS (doc) = HOL +
-  options [document_variants = "demo_llncs",
-    document_build = "pdflatex", document_heading_prefix = "", document_comment_latex]
+  options [document_variants = "demo_llncs"]
   theories
     Document
   document_files (in "$ISABELLE_LLNCS_HOME")