add background to hints section in docs
@@ -426,6 +426,8 @@ Some possible uses for these attributes are:
align the text if its width is shorter than `minimal_width`.
* `separator` and `separator_block_width` can be used to remove the
vertical bar that is separating modules.
+* `background` can be used to set an alternative background color for the
+ module. supports RGBA if your i3bar version does.
* `markup` can be set to `"none"` or `"pango"`.
`Pango markup
<https://developer.gnome.org/pango/stable/PangoMarkupFormat.html>`_
