Build release tar and include hash

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

cmd/containerd-release/template.go

@@ -0,0 +1,35 @@
+package main
+
+const releaseNotes = `Welcome to the release of containerd {{.Version}}!
+{{if .PreRelease}}
+*This is a pre-release of containerd*
+{{- end}}
+
+{{.Preface}}
+
+Please try out the release binaries and report any issues at
+https://github.com/containerd/containerd/issues.
+
+{{range  $note := .Notes}}
+### {{$note.Title}}
+
+{{$note.Description}}
+{{- end}}
+
+### Contributors
+{{range $contributor := .Contributors}}
+* {{$contributor}}
+{{- end}}
+
+### Changes
+{{range $change := .Changes}}
+* {{$change.Commit}} {{$change.Description}}
+{{- end}}
+
+### Dependency Changes
+
+Previous release can be found at [{{.Previous}}](https://github.com/containerd/containerd/releases/tag/{{.Previous}})
+{{range $dep := .Dependencies}}
+* {{$dep.Previous}} -> {{$dep.Commit}} **{{$dep.Name}}**
+{{- end}}
+`