Issue #15501: Document exception classes in subprocess module.

Initial patch by Anton Barkovsky.
diff --git a/Misc/ACKS b/Misc/ACKS
index 39ba2a9..56d5765 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -44,6 +44,7 @@
 Matt Bandy
 Michael J. Barber
 Chris Barker
+Anton Barkovsky
 Nick Barnes
 Quentin Barnes
 Richard Barran