Docs need to be fixed for Shannon diversity. should include evenness

[JTFouquier]

Comments
Shannon diversity includes evenness and this is not reflected in the docs (might have been accidentally removed). Users are learning these things from Q2 docs, so should be updated soon. The biology here is confirmed by various resources and @nbokulich. Thanks!

References
https://docs.qiime2.org/2019.4/tutorials/moving-pictures/#alpha-and-beta-diversity-analysis
https://forum.qiime2.org/t/alpha-and-beta-diversity-explanations-and-commands/2282