Update AUTHORS.txt, CONTRIBUTORS.txt and README.md

[RosaWagner]

• AUTHORS.txt : Names listed there is what will appear as "designers" in the GF specimen page. It should include the original author Matt Bailey and all contributing designers. You can also have "The League Of" as a collective.
• CONTRIBUTORS.txt : people who contributed on a non-design level.
• README.md: General update + include the original repo with mention of Matt Bailey.

[RosaWagner]

I guess no one is receiving notification from this repo. friendly ping to @sursly cause if we don't merge the font today in google/repo, it won't be pushed to prod before a month or more

[sursly]

@alerque @micahbrich ☝️

[micahbrich]

This stuff is superfluous and I must not have been paying enough attention to whomever brought it in. I'm gonna work on getting rid of it. Also Matt's was originally a fork of ours, I'm gonna try to correct that misinformation wherever it lives.

[alerque]

Not it's not superfluous, this meta data is used various places. It shouldn't be removed, it should be fixed. But correct about the misinformation out there about the original vs. fork. Google Fonts gets that mixed up quite a bit.

(I was on extended travels when this notification came in and it got lost in the post-trip-dog-pile.)