Docs: add floodwaiter example

[TeaDove]

Floodwaiter example added with new RunMiddleware option.

(not sure if RunMiddleware function is written correctly, but in my project it works as expected)

[TeaDove]

@celestix I think flood waiter example is very important, cause flood-waiter almost always is mandatory.
If you want, I can add waiter to new seperate example

[celestix]

@celestix I think flood waiter example is very important, cause flood-waiter almost always is mandatory.
If you want, I can add waiter to new seperate example

Hello, I think you're right. It would be better to keep it as a separate example.

[TeaDove]

@celestix done it!

[celestix]

Thank you for this valuable addition to the examples!