Issue #15677: Document that zlib and gzip accept a compression level of 0 to mean 'no compression'.

Patch by Brian Brazil.
diff --git a/Misc/NEWS b/Misc/NEWS
index 96c8614..d5a048e 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -556,6 +556,9 @@
 Documentation
 -------------
 
+- Issue #15677: Document that zlib and gzip accept a compression level of 0 to
+  mean 'no compression'. Patch by Brian Brazil.
+
 - Issue #8040: added a version switcher to the documentation.  Patch by
   Yury Selivanov.