Issue #21545: Add .pop example and tweak comment about pure mutation methods.
Patch prepared by David Harrigan.
diff --git a/Misc/ACKS b/Misc/ACKS
index c8c3880..9ae3341 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -506,6 +506,7 @@
 Lynda Hardman
 Derek Harland
 Jason Harper
+David Harrigan
 Brian Harring
 Jonathan Hartley
 Travis B. Hartwell