Document hack/tag_release.sh

docs/contributors/releasing_minikube.md

@@ -61,15 +61,8 @@ Merge the output into CHANGELOG.md. See [PR#3175](https://github.com/kubernetes/
 
 NOTE: Confirm that all release-related PR's have been submitted before doing this step. 
 
-Do this in a direct clone of the upstream kubernetes/minikube repository (not your fork!):
-
-```
-version=<new version number>
-git fetch
-git checkout master
-git pull
-git tag -a v$version -m "$version Release"
-git push origin v$version
+```shell
+hack/tag_release.sh <new version number>
 ```
 
 ## Build the Release