Add documentation guide line

There are various patterns of title headings at now.
It is better to unify the pattern of headings.
This commit adds the guideline.

Change-Id: I22563e6f480351762b22432ec6049b2ac5d8a2fe

doc/source/about.rst

@@ -0,0 +1,37 @@
+================
+About this guide
+================
+
+This page describes the conventions and tips on writing this guide itself.
+
+The guide is written in reStructuredText (RST) markup syntax with Sphinx
+extensions. Most convenstions follow
+`those of the openstack-manuals project
+<http://docs.openstack.org/contributor-guide/rst-conv.html>`__.
+
+The followings are useful links when writing documents in RST.
+
+* `Sphinx documentation <http://sphinx.readthedocs.io/en/latest/rest.html>`__
+* `Quick reStructuredText <http://docutils.sourceforge.net/docs/user/rst/quickref.html>`__
+
+Titles
+------
+
+The convention for heading levels is as follows::
+
+   =========
+   Heading 1
+   =========
+
+   Overline and underline with equal signs for heading 1 sections.
+   This level is reserved for the title in a document.
+
+   Heading 2
+   ---------
+
+   Underline with dashes for heading 2 sections.
+
+   Heading 3
+   ~~~~~~~~~
+
+   Underline with tildas for heading 3 sections.

doc/source/index.rst

@@ -29,6 +29,7 @@ Contents
    translation_stats
    i18n_team_meeting
    infra
+   about
 
 .. _label-i18n-team-contact: