etc/options

--- a/etc/options	Mon May 17 23:38:16 2021 +0200
+++ b/etc/options	Tue May 18 15:17:55 2021 +0200
@@ -15,6 +15,8 @@
   -- "default command tags (separated by commas)"
 option document_build : string = "lualatex"
   -- "document build engine (e.g. lualatex, pdflatex, build)"
+option document_logo : string = ""
+  -- "generate named instance of Isabelle logo (underscore means unnamed variant)"
 
 option thy_output_display : bool = false
   -- "indicate output as multi-line display-style material"