Add details about optional Advanced Tutorial Session for participants

Author: a-latyshev

conference/2026.md

@@ -94,6 +94,9 @@ changes are needed.
 - The registration fee includes: conference activities, coffee breaks,
   conference dinner, and social events. The registration fee does not include
   lunches, and it is non-refundable.
+- All participants are welcome to attend an optional Advanced Tutorial Session
+  in the morning on Wednesday, 17 June. More details are available in the
+  [conference programme](pages_2026/programme.md).
 
 ## Conference venue