add download button

app.py

@@ -74,6 +74,13 @@ def molecule(input_pdb):
 
                 document.body.removeChild(element);
                 }
+
+            document.getElementById("dwn-btn").addEventListener("click", function(){
+                var text = document.getElementById("text-val").value;
+                var filename = "result.pdb";
+                
+                download(filename, text);
+            }, false);
         </script>
     """