Add posibility to just copy the DOI

[jorgman1]

Is your suggestion for improvement related to a problem? Please describe.
I'm currently writing a review for a paper, where I usually provide DOIs to facilitate authors retrieving the references. To copy the DOI I need to open the respective entry, navigate to the correct tab and then copy it.

Describe the solution you'd like
It would be helpful to include a further entry in the copy menu (right click + shortcuts) to quickly copy the DOI.

[jorgman1]

Thanks for the quick fix. :)
It might be better to name the field just "Copy DOI" instead of "Copy DOI url", because it just copies the text in the DOI field without appending https://doi.org/. (Which is really fine!)