fixup! CP-310090 Stunnel lib: Expose unix socket path for TLS proxy

Author: changlei-li

ocaml/libs/stunnel/stunnel.mli

@@ -102,7 +102,11 @@ val with_client_proxy_systemd_service :
 
 module UnixSocketProxy : sig
   (** Handle for a long-running stunnel proxy that exposes TLS connection
-      via a UNIX socket file. *)
+      via a UNIX socket file.
+      This module allows to create stunnel clients. But in XAPI, if you are
+      finding a stunnel client to use, you probably should use stunnel_cache.ml.
+      Stunnel instances there are managed and reused.
+      *)
   type t
 
   val socket_path : t -> string