#10999: Add missing documentation for chflags constants to stat module docs

Patch by Michal Nowikowski.
diff --git a/Misc/ACKS b/Misc/ACKS
index 3cb7667..9ec0fc9 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -584,6 +584,7 @@
 Tim Northover
 Joe Norton
 Neal Norwitz
+Michal Nowikowski
 Nigel O'Brian
 Kevin O'Connor
 Tim O'Malley