Add TODO

src/side_by_side.rs

@@ -233,6 +233,7 @@ fn highlight_as_novel(
         // If this is a blank line without a corresponding line on the
         // other side, highlight it too. This helps highlight novel
         // blank lines.
+        // TODO: consider whitespace-only lines here too.
         if line_content == Some(&"".into()) && opposite_line_num.is_none() {
             return true;
         }