bpo-27413: json.tool: Add --no-ensure-ascii option. (GH-17472)

diff --git a/Doc/library/json.rst b/Doc/library/json.rst
index 23e39e9..573ec1c 100644
--- a/Doc/library/json.rst
+++ b/Doc/library/json.rst
@@ -732,6 +732,12 @@
 
    .. versionadded:: 3.5
 
+.. cmdoption:: --no-ensure-ascii
+
+   Disable escaping of non-ascii characters, see :func:`json.dumps` for more information.
+
+   .. versionadded:: 3.9
+
 .. cmdoption:: --json-lines
 
    Parse every input line as separate JSON object.