bpo-31793: Doc: Specialize smart-quotes for Japanese (GH-4006)

(cherry picked from commit 5a66c8a64d180b5f3c80307924adaec53cc8faa3)
diff --git a/Doc/docutils.conf b/Doc/docutils.conf
new file mode 100644
index 0000000..bda4f5d
--- /dev/null
+++ b/Doc/docutils.conf
@@ -0,0 +1,2 @@
+[restructuredtext parser]
+smartquotes-locales: ja: ""''