add intersphinx inventory

docs/conf.py

@@ -35,7 +35,7 @@ from glances import __version__
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
 #extensions = ['sphinxcontrib.autohttp.bottle']
-extensions = []
+extensions = ['sphinx.ext.intersphinx']
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']