Issue #25626: Add news to 3.6 section

Misc/NEWS

@@ -95,6 +95,13 @@ Core and Builtins
 Library
 -------
 
+- Issue #25626: Change three zlib functions to accept sizes that fit in
+  Py_ssize_t, but internally cap those sizes to UINT_MAX.  This resolves a
+  regression in 3.5 where GzipFile.read() failed to read chunks larger than 2
+  or 4 GiB.  The change affects the zlib.Decompress.decompress() max_length
+  parameter, the zlib.decompress() bufsize parameter, and the
+  zlib.Decompress.flush() length parameter.
+
 - Issue #25583: Avoid incorrect errors raised by os.makedirs(exist_ok=True)
   when the OS gives priority to errors such as EACCES over EEXIST.