ReadME citations not up to date

[Nikoleta-v3]

Hello! So looking at the Publications on the README.md they do not seem to be up to date with: https://github.com/Axelrod-Python/Axelrod/blob/master/citations.md.

Could we possibly just redirect people there? @marcharper I know that you are collecting the citations.
Do you want to let me know how and I can close this issue?

[marcharper]

If you prefer redirecting that's fine with me. I was just checking Google Scholar occasionally and wasn't necessarily trying to keep the readme in sync with citations.md.

[marcharper]

Speaking of which here are some new ones:

• https://arxiv.org/pdf/1809.10007.pdf
• https://link.springer.com/chapter/10.1007/978-3-030-00350-0_30

and one that cites the strategy list in the docs:

• https://link.springer.com/chapter/10.1007/978-3-319-91467-1_24

[marcharper]

Also our latest paper is officially live now at PLOS :)