fix: wrong checkout command in documentation (#894)

Signed-off-by: Pasha Kostohrys <pavel@codefresh.io>

Author: pasha-codefresh

docs/contributing/releasing.md

@@ -17,7 +17,7 @@ Then create a release branch:
 
 ```
 git clone git@github.com:argoproj-labs/argocd-image-updater.git
-git branch -b release-0.13
+git checkout -b release-0.13
 git push origin release-0.13
 ```