✏️ Create 'copy to clipboard' button to markdown editor

[Thenlie]

Is your feature request related to a problem? Please describe.
As a user, I would like to be able to copy my generated README directly to my clipboard without needing to highlight the entire file.

Describe the solution you'd like
There should be a 'copy to clipboard' button on the top pane of the markdown editor. When presses, it should copy the entire editor contents to the users clipboard.

Additional context
This can be done via a custom toolbar https://github.com/uiwjs/react-md-editor#custom-toolbars. Please ensure all buttons currently on the toolbar remain.

[Thenlie]

Green Arrow: Where the button would ideally live
Blue Box: The contents that should be copied by clicking on the button