Update "About" section on the front page to show support for Postgres 16 as well as main README

[Thomas Nyberg]

I'm talking about this section on the right as well as the README:

It looks like this doesn't support Postgres 16, but I see it does:

#428
#437

I guess the main distributions aren't packaging Postgres 16 yet, but still if 16 is supported I think it should be mentioned. I had someone last week recommend I avoid this extension because they incorrectly believed the project was dead due to the "fact" that Postgres 16 supported hadn't been added yet.

I could open a PR changing some of the docs, but don't know how to change the About section (which is the most prominent).

[Noah Misch]

+1. Also, that section contains URL https://www.2ndquadrant.com/en/resources/pglogical/, which reaches "Page not found".