Update README.md with periods on initials

[lawrennd]

Hi, thanks for the great tool!

I think it's recommended practice to always add the period to abbreviate initials.

See e.g. https://clauswilke.com/blog/2015/10/02/bibtex/

I've added periods in your README.md in this pull request.

Apologies for the pedancy ... I may be fighting a long battle with this ... it gives me headaches when people don't do this for a proceedings I edit ... and then initials are incorrectly rendered ...