Update citation / credit info

[msonderegger]

On this page:
https://polyglotdb-michaelhaaf-dev.readthedocs.io/en/latest/introduction.html

and on the readme for this repository:
https://github.com/MontrealCorpusTools/PolyglotDB/

Michael Haaf (@michaelhaaf) should be added as a contributor, and the citation of the program should be changed to:

McAuliffe, Michael, Elias Stengel-Eskin, Michaela Socolof, Arlie Coles, Michael Haaf, Sarah Mihuc, Morgan Sonderegger (2022). PolyglotDB [Computer program]. Version 1.2.1, retrieved 27 July, 2022 from https://github.com/MontrealCorpusTools/PolyglotDB.

and the following text should be added on both pages:

"
If you use PolyglotDB's formant measurement algorithm, please also cite:

Jeff Mielke, Erik Thomas, Joe Fruehwald, Jane Stuart-Smith, M. Sonderegger, Robin Dodsworth, and Michael McAuliffe. (2019) Age vectors vs. axes of intraspeaker variation in vowel formants measured automatically from several English speech corpora. Proceedings of the 19th International Congress of Phonetic Sciences.
"