Add README with CLI usage descriptions

README.md

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+# Scalar Admin for Kubernetes
+
+Scalar Admin for Kubernetes is a tool that creates a paused state for ScalarDB or ScalarDL in a Kubernetes environment. You can use such a paused state to take backups easily and consistently across multiple diverse databases.
+
+## Usage of the CLI tool
+
+```console
+Usage: scalar-admin-for-kubernetes-cli [-h] [-d=<pauseDuration>]
+                                       [-n=<namespace>] -r=<helmReleaseName>
+                                       [-w=<maxPauseWaitTime>] [-z=<zoneId>]
+Scalar Admin pause tool for the Kubernetes environment
+  -d, --pause-duration=<pauseDuration>
+                             The duration of the pause period by millisecond.
+                               5000 (5 seconds) by default.
+  -h, --help                 Display the help message.
+  -n, --namespace=<namespace>
+                             Namespace that Scalar products you want to pause
+                               are deployed. `default` by default.
+  -r, --release-name=<helmReleaseName>
+                             Helm's release name that you specify when you run
+                               the `helm install <RELEASE_NAME>` command. You
+                               can see the <RELEASE_NAME> by using the `helm
+                               list` command.
+  -w, --max-pause-wait-time=<maxPauseWaitTime>
+                             The max wait time (in milliseconds) until Scalar
+                               products drain outstanding requests before they
+                               pause. If omitting this option, the max wait
+                               time will be the default value defined in the
+                               products. Most Scalar products have the default
+                               value of 30 seconds.
+  -z, --time-zone=<zoneId>   Specify a time zone ID, e.g., Asia/Tokyo, to
+                               output successful paused period. Note the time
+                               zone ID is case sensitive. Etc/UTC by default.
+```
+
+## Run the CLI tool in a Kubernetes environment
+
+The `scalar-admin-for-kubernetes` CLI tool executes Kubernetes APIs in its internal processes. To run those Kubernetes APIs, you must run the `scalar-admin-for-kubernetes` CLI tool as a pod on the Kubernetes environment by following the steps below:
+
+1. Create three Kubernetes resources (`Role`, `RoleBinding`, and `ServiceAccount`), replacing the contents in the angle brackets as described:
+
+   * Role
+
+     ```yaml
+     apiVersion: rbac.authorization.k8s.io/v1
+     kind: Role
+     metadata:
+       name: scalar-admin-for-kubernetes-role
+       namespace: <YOUR_NAMESPACE>
+     rules:
+       - apiGroups: ["", "apps"]
+         resources: ["pods", "deployments", "services"]
+         verbs: ["get", "list"]
+     ```
+
+   * RoleBinding
+
+     ```yaml
+     apiVersion: rbac.authorization.k8s.io/v1
+     kind: RoleBinding
+     metadata:
+       name: scalar-admin-for-kubernetes-rolebinding
+       namespace: <YOUR_NAMESPACE>
+     subjects:
+       - kind: ServiceAccount
+         name: scalar-admin-for-kubernetes-sa
+     roleRef:
+       kind: Role
+       name: scalar-admin-for-kubernetes-role
+       apiGroup: rbac.authorization.k8s.io
+     ```
+
+   * ServiceAccount
+
+     ```yaml
+     apiVersion: v1
+     kind: ServiceAccount
+     metadata:
+       name: scalar-admin-for-kubernetes-sa
+       namespace: <YOUR_NAMESPACE>
+     ```
+
+1. Mount the `ServiceAccount` resource on the `scalar-admin-for-kubernetes` pod, replacing the contents in the angle brackets as described:
+
+   * Pod
+
+     ```yaml
+     apiVersion: v1
+     kind: Pod
+     metadata:
+       name: scalar-admin-for-kubernetes
+       namespace: <YOUR_NAMESPACE>
+     spec:
+       serviceAccountName: scalar-admin-for-kubernetes-sa
+       containers:
+       - name: scalar-admin-for-kubernetes
+         image: ghcr.io/scalar-labs/scalar-admin-for-kubernetes:1.0.0
+         command:
+           - java
+           - -jar
+           - /app.jar
+           - -r
+           - <HELM_RELEASE_NAME>
+           - -n
+           - <SCALAR_PRODUCT_NAMESPACE>
+           - -d
+           - <PAUSE_DURATION>
+           - -z
+           - <TIMEZONE>
+     ```
+
+## Run the CLI tool in a Kubernetes environment by using a Helm Chart
+
+Coming soon.