doc: Add "internationalization" to the usage guide

This is added to the new "advanced" subsection.

Signed-off-by: Stephen Finucane <stephen@that.guru>

doc/contents.rst

@@ -14,10 +14,10 @@ Sphinx documentation contents
    usage/configuration
    usage/builders/index
    usage/extensions/index
+   usage/advanced/intl
 
    intro
    man/index
-   intl
    theming
    setuptools
    templating

doc/usage/advanced/intl.rst

@@ -9,7 +9,7 @@ Complementary to translations provided for Sphinx-generated messages such as
 navigation bars, Sphinx provides mechanisms facilitating *document* translations
 in itself.  See the :ref:`intl-options` for details on configuration.
 
-.. figure:: translation.png
+.. figure:: /_static/translation.png
    :width: 100%
 
    Workflow visualization of translations in Sphinx.  (The stick-figure is taken