Doc: add backtick to scheme example with comma.

diff --git a/Documentation/extending/programming-interface.itely b/Documentation/extending/programming-interface.itely
index 4bae49aa4a62ba75e9dba5d2c6f710822684f43f..3806d35dc4c2352fe6330aee9b8ef10d9a8e4605 100644 (file)
--- a/Documentation/extending/programming-interface.itely
+++ b/Documentation/extending/programming-interface.itely
@@ -894,7 +894,7 @@ can be inserted with a grob closure.  Here is a setting from
 @code{AccidentalSuggestion},
 
 @example
-(X-offset .
+`(X-offset .
   ,(ly:make-simple-closure
     `(,+
         ,(ly:make-simple-closure