Update README

README.md

@@ -18,10 +18,21 @@ type OneOfstringprojectResponse interface{}
 ````
 
 ## Usage
+### Build client by token
 ```go
 // Build client
-config := openapi.NewConfiguration()
-client, err := keystone.NewClient(config)
+client, err := keystone.NewDefaultClientByToken("a_keystone_token")
+if err != nil {
+    panic(err)
+}
+
+// API Call
+resp, r, err := client.DomainApi.ListDomains(context.TODO()).Execute()
+```
+### Build client by password
+```go
+// Build client
+client, err := keystone.NewDefaultClient()
 if err != nil {
     panic(err)
 }
@@ -47,21 +58,9 @@ resp, r, err := client.DomainApi.ListDomains(context.TODO()).Execute()
 ### How to change the server configuration?
 #### Default
 The client uses the first server (index=0) defined in OAS by default.
-
-#### Change server index
-By specifying the server index, client will use corresponding server configuration defined in OAS.
-```go
-// Build the client
-serverIndex := 1
-config := openapi.NewConfiguration()
-client, err := keystone.NewClientWithServerIndex(config, serverIndex)
-
-// Authentication is omitted.
-
-// API Call
-ctx := context.WithValue(context.TODO(), openapi.ContextServerIndex, serverIndex)
-resp, r, err := client.DomainApi.ListDomains(ctx).Execute()
-
+```yaml
+- description: Service domain
+  url: http://keystone-api.openstack.svc.cluster.local
 ```
 
 #### Change manually in code
@@ -70,8 +69,6 @@ Just edit the `config` object.
 config := openapi.NewConfiguration()
 config.Servers = openapi.ServerConfigurations{{
     URL:         "localhost:8000",
-    Description: "local test",
-    Variables:   nil,
 }}
 client, err := keystone.NewClient(config)
 ```