Fix broken link to release-tool
by containerd's release tool but refer to previous release files for style
and format help. Name the file using the version, for rc add an `-rc` suffix.
When moving from rc to final, the rc file may just be renamed and updated.
- See [release-tool](https://github.com/containerd/project/tree/master/cmd/release-tool)
+ See [release-tool](https://github.com/containerd/release-tool)
2. Update the version file at `https://github.com/containerd/containerd/blob/master/version/version.go`
