feat(mdbook): add tui theme

Author: ashleygwilliams

src/site/mdbook.rs

@@ -86,6 +86,7 @@ impl AxomdbookTheme {
             Theme::Dark => Some(Axo),
             Theme::Hacker => Some(Hacker),
             Theme::Cupcake => Some(Cupcake),
+            Theme::Tui => None,
         }
     }