Issue #15501: Document exception classes in subprocess module.

Initial patch by Anton Barkovsky.
diff --git a/Misc/ACKS b/Misc/ACKS
index b255ed2..4dce609 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -56,6 +56,7 @@
 Michael J. Barber
 Nicolas Bareil
 Chris Barker
+Anton Barkovsky
 Nick Barnes
 Quentin Barnes
 David Barnett