added author

--- a/src/HOL/Library/FSet.thy	Fri May 26 09:56:20 2023 +0200
+++ b/src/HOL/Library/FSet.thy	Fri May 26 09:59:06 2023 +0200
@@ -2,6 +2,7 @@
     Author:     Ondrej Kuncar, TU Muenchen
     Author:     Cezary Kaliszyk and Christian Urban
     Author:     Andrei Popescu, TU Muenchen
+    Author:     Martin Desharnais, MPI-INF Saarbruecken
 *)
 
 section \<open>Type of finite sets defined as a subtype of sets\<close>