Add Chris Rebert to ACKS for issue 6760 Popen doc improvements.
diff --git a/Misc/ACKS b/Misc/ACKS
index 3eb9c49..b5c3dc6 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -612,6 +612,7 @@
 Antti Rasinen
 Eric Raymond
 Edward K. Ream
+Chris Rebert
 Marc Recht
 John Redford
 Terry Reedy