Tag as `x.y.z` without `v` prefix

Signed-off-by: Nicolas De Loof <[email protected]>

Close https://github.com/docker/compose/issues/7168

script/release/README.md

@@ -5,5 +5,5 @@ The release process is fully automated by `Release.Jenkinsfile`.
 ## Usage
 
 1. edit `compose/__init__.py` to set release version number
-1. commit and tag as `v{major}.{minor}.{patch}`
+1. commit and tag as `{major}.{minor}.{patch}`
 1. edit `compose/__init__.py` again to set next development version number