add title for structure

components/OperonStructure.vue

@@ -276,6 +276,9 @@ function drawStructure(operonGroup: d3.Selection<SVGGElement, any, SVGElement |
                 // img group
                 gStructure
                     .append("image")
+                gStructure
+                    .append("title")
+
                 return gStructure
             },
             update => update,
@@ -293,7 +296,7 @@ function drawStructure(operonGroup: d3.Selection<SVGGElement, any, SVGElement |
         .attr("width", d => d.width)
         .attr("height", d => d.height)
         .attr("preserveAspectRatio", "xMidYMid meet")
-
+    structureSelection.select("title").text(d => `${d.gene} | ${d.size} aa`)
 
 
 }