docs/sphinx: set navigation_with_keys=True

Allow navigating to the previous/next page using the keyboard's left and
right arrows. I wish this would be the default, and that the themes
would provide more key navigation, but that doesn't seem on the roadmap.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

docs/conf.py

@@ -166,6 +166,7 @@
 if LooseVersion(sphinx_rtd_theme.__version__) >= LooseVersion("0.4.3"):
     html_theme_options = {
         "style_nav_header_background": "#802400",
+        "navigation_with_keys": True,
     }
 
 html_logo = os.path.join(qemu_docdir, "../ui/icons/qemu_128x128.png")