update link in root README
update link in root README

The old containerd link is dead.

Signed-off-by: Peng Tao <39d8af57313740070ea49547576f55682fe5221a@gmail.com>

gao-feng/runv,hyperhq/runv,gao-feng/runv,gao-feng/runv,laijs/runv,bergwolf/runv,gnawux/runv,jinfenw/runv,laijs/runv,gnawux/runv,bergwolf/runv,jinfenw/runv,bergwolf/runv,hyperhq/runv,jinfenw/runv,laijs/runv,gnawux/runv,hyperhq/runv