Specify kubespray version for docker run (#9519)

When operating kubespray from kubespray image with docker run,
we need to checkout the specific kubespray version as the same as
the image, because the sample inventory contains kubernetes version
and the version of master branch could not be supported on the released
kubespray, for example.

README.md

@@ -57,6 +57,7 @@ A simple way to ensure you get all the correct version of Ansible is to use the
 You will then need to use [bind mounts](https://docs.docker.com/storage/bind-mounts/) to get the inventory and ssh key into the container, like this:
 
 ```ShellSession
+git checkout v2.20.0
 docker pull quay.io/kubespray/kubespray:v2.20.0
 docker run --rm -it --mount type=bind,source="$(pwd)"/inventory/sample,dst=/inventory \
   --mount type=bind,source="${HOME}"/.ssh/id_rsa,dst=/root/.ssh/id_rsa \