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

Patch by Michal Nowikowski.
diff --git a/Misc/ACKS b/Misc/ACKS
index 023fe94..9d4be3f 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -578,6 +578,7 @@
 Tim Northover
 Joe Norton
 Neal Norwitz
+Michal Nowikowski
 Nigel O'Brian
 Kevin O'Connor
 Tim O'Malley