Enable release notes translation

Releasenote translation publishing is being prepared. 'locale_dirs'
needs to be defined in conf.py to generate translated version of the
release notes.

Note that this repository might not get translated release notes - or
no translations at all - but we add the entry here nevertheless to
prepare for it.

Change-Id: If6ecada10cd963d77eb233e109266ecc0673958a

releasenotes/source/conf.py

@@ -249,3 +249,6 @@ texinfo_documents = [
 
 # If true, do not generate a @detailmenu in the "Top" node's menu.
 # texinfo_no_detailmenu = False
+
+# -- Options for Internationalization output ------------------------------
+locale_dirs = ['locale/']