Point to example in Picos_select library

Author: polytypic

lib/picos_sync/picos_sync.mli

@@ -165,6 +165,8 @@ module Event : sig
       offer or request that might be accepted or succeed, but is cancelable if
       some other event happens first.
 
+      See the {!Picos_select} library for an example.
+
       ℹ️ This module intentionally mimics the
       {{:https://ocaml.org/manual/5.2/api/Event.html} [Event]} module provided
       by the OCaml POSIX threads library. *)