Add Alphafold citation to protein structure visualizer

[davereinhart]

https://www.ebi.ac.uk/training/online/courses/navigating-alphafold-database/citing-the-database/

[bencap]

Although we mention and link to the Alphafold database in the docs, it would also be worthwhile to explicitly cite it in this format there too.

https://mavedb.org/docs/mavedb/finding-data/visualizations.html?h=protein+st#protein-structure-viewer