feat: 'addon' property support

..to be able to render something like OK button to timepicker:
```
            <TimePicker
              allowEmpty={false}
              addon={panel => {
                return (
                  <div className="row">
                    <a role="button" className="btn btn-sm btn-default" onClick={() => panel.close()}>
                      {__('OK')}
                    </a>
                  </div>
                )
              }}
            />

```

1 files changed, 1 insertions, 0 deletions

diff --git a/README.md b/README.md
index 3ae31aa..5ec960c 100644
--- a/README.md
+++ b/README.md
@@ -67,6 +67,7 @@ API
 | disabledSeconds         | Function                          | disabled second options                       |                                                                                            |
 | hideDisabledOptions     | Boolean                           | whether hide disabled options                 |                                                                                            |
 | onChange                | Function                          | null                                          | called when select a different value                                                       |
+| addon                   | Function                          | nothing                                       | called from timepicker panel to render some addon to its bottom, like an OK button. Receives panel instance as parameter, to be able to close it like `panel.close()`.|
 | placement               | String                            | bottomLeft                                    | one of ['left','right','top','bottom', 'topLeft', 'topRight', 'bottomLeft', 'bottomRight'] |
 | transitionName          | String                            | ''                                            |                                                                                            |