[ADD] changelog file with support of i18n_extra folder

bzr revid: mat@openerp.com-20130813140300-g9amgza8h9w1lt4j

doc/changelog.rst

+.. _changelog:
+
+Changelog
+=========
+
+`7.0`
+-----
+
+- Support of repository ``i18n_extra`` for additional (and manual) translation files