Update Message and Notification documentation

[rsrogers4]

• I have searched the issues of this repository and believe that this is not a duplicate.

What problem does this feature solve?

I could not figure out how to make Message or Notification work until I realized that a) unlike all the other Vue components, Notification and Message need to use lower-case when importing (e.g., import { message} from "ant-design-vue"), and that b) setting the Vue.prototype.$message and Vue.prototype.$notification is mandatory (e.g., Vue.prototype.$message = message;).

PS: The same comments apply to modal.

What does the proposed API look like?

It would be wonderful if the documentation explained these requirements so that beginners can more easily use Message and Notification.

[tangjinzhou]

We will improve the documentation. Of course, you can also directly pr.

[github-actions]

This issue is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 7 days

[github-actions]

This issue has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.