docs: opacity prop

Author: gabrieljablonski

docs/docs/options.mdx

@@ -122,6 +122,7 @@ import { Tooltip } from 'react-tooltip';
 | `afterHide`        | `function`                 | no       |                           |                                                                                                                                   | A function to be called after the tooltip is hidden                                                                                                             |
 | `middlewares`      | `Middleware[]`             | no       |                           | array of valid `floating-ui` middlewares                                                                                          | Allows for advanced customization. Check the [`floating-ui` docs](https://floating-ui.com/docs/middleware) for more information                                 |
 | `border`           | `CSSProperties['border']`  | no       |                           | a CSS border style                                                                                                                | Change the style of the tooltip border (including the arrow)                                                                                                    |
+| `opacity`          | `CSSProperties['opacity']` | no       | `0.9`                     | a CSS opacity value                                                                                                               | Change the opacity of the tooltip                                                                                                                               |
 
 ### Envs