README: Update for meson

Also, update the RFC numbers that are implemented.
4 jobs for master in 15 minutes and 10 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #2624019
docker windows 1809
build msvc amd64

00:05:15

passed #2624020
docker windows 1809
build msvc x86

00:04:01

passed #2624018
docker windows 1809
build msys2

00:13:47

 
  Test
passed #2624021
submit-to-coverity

00:01:23