Update README.md

Author: hinodi

README.md

@@ -50,6 +50,7 @@ You also use CircularProgress without inner Circle
 | endDeg          | End degree of CircularProgress, where animation end (0-360), greater than startDeg                                               | Number |          |                                 360                                  |
 | radius          | Radius of outer CircularProgress                                                                                                 | Number |          |                                 100                                  |
 | innerRadius     | Radius of inner CircularProgress                                                                                                 | Number |          |                                  80                                  |
+| innerBackgroundColor    | Background color of inner CircularProgress                                                                                                 | String |          |                                  transparent                                  |
 | duration        | Time in ms, animation processing during this time. Actually animation time is duration / (endDeg - startDeg) smaller than radius | Number |          |                                 1000                                 |
 | children        | The children to render inside this component                                                                                     | Node   |          |                                `null`                                |
 | style           | The custom styling which will be applied to the container of the `children`                                                      | Style  |          |                                `null`                                |