Readme: Add info how to run tests

8 jobs for master in 3 minutes and 5 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #11440
amd64 debian
build-debian

00:00:30

passed #11444
debian aarch64
build-debian-aarch64

00:01:37

passed #11445
debian clang5 aarch64
build-debian-aarch64-clang-5

00:01:16

passed #11441
amd64 debian
build-debian-static

00:00:30

passed #11447
debian aarch64
build-debian-werror

00:01:05

passed #11446
macos
build-macos

00:00:24

passed #11442
win32
build-win32

00:00:28

passed #11443
win64
build-win64

00:00:33