a small fix of minikube tutorial (#2120)

* fix minikube tutorial

* Update elasticdl_local.md

* fix format

Co-authored-by: Yi Wang <[email protected]>

Author: QiJune

docs/tutorials/elasticdl_local.md

@@ -34,7 +34,10 @@ Clone elasticdl repo for model zoo and some scripts.
 git clone https://github.com/sql-machine-learning/elasticdl.git
 ```
 
-### Setup Kubernetes related environment
+### Start Kubernetes Cluster
+
+We start minikube with a command-line option `--mount-string`,
+which mounts the host directory `$DATA_PATH` to `/data` path in all minikube containers.
 
 ```bash
 export DATA_PATH={a_folder_path_to_store_training_data}
@@ -44,8 +47,6 @@ kubectl apply -f elasticdl/manifests/elasticdl-rbac.yaml
 eval $(minikube docker-env)
 ```
 
-Mount the host path $DATA_PATH to /data of minikube
-
 ### Build the Docker image for distributed training
 
 ```bash
@@ -69,9 +70,12 @@ docker run --rm -it \
   -v $HOME/.keras/datasets:/root/.keras/datasets \
   -v $PWD:/work \
   -w /work elasticdl/elasticdl:dev \
-  bash -c "scripts/gen_dataset.sh $DATA_PATH"
+  bash -c "scripts/gen_dataset.sh data"
+cp -r data/* $DATA_PATH
 ```
 
+We generate datasets and copy them to `$DATA_PATH`.
+
 ### Summit a training job
 
 We use the following command to submit a training job: