Add SIAM News article to publications.

[marcfehling]

We should mention the SIAM News article [1] about deal.II in the publications section on our website. I would suggest to do it not only with a link, but also as a copy on our server for future preservation (in some format, e.g. pdf?).

[1] https://www.siam.org/publications/siam-news/articles/supporting-computational-science-and-engineering-the-creation-of-widely-used-software-in-industrial-and-applied-mathematics/