Documentation: Add HOWTO Japanese translation into rst based build system

This commit adds Japanese translation of HOWTO document into rst based
documentation build system with updates.
Signed-off-by: Tsugikazu Shibata <tshibata@ab.jp.nec.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/index.rst

@@ -76,6 +76,14 @@ Chinese translations
 
    translations/zh_CN/index
 
+Japanese translations
+---------------------
+
+.. toctree::
+   :maxdepth: 1
+
+   translations/ja_JP/index
+
 Indices and tables
 ==================
 

Documentation/translations/ja_JP/index.rst

+.. raw:: latex
+
+        \renewcommand\thesection*
+        \renewcommand\thesubsection*
+
+Japanese translations
+=====================
+
+.. toctree::
+   :maxdepth: 1
+
+   howto