Update readme for multi namespace support (#2416)

Update readme for multi namespace support

Author: Quinn-With-Two-Ns

temporal-spring-boot-autoconfigure/README.md

@@ -256,4 +256,61 @@ public class Test {
 }
 ```
 
+# Running Multiple Name Space (experimental)
 
+Along with the root namespace, you can configure multiple non-root namespaces in the application.yml file. Different namespaces can have different configurations including but not limited to different connection options, registered workflows/activities, data converters etc.
+
+```yml
+spring.temporal:
+    namespaces:
+      - namespace: assign
+        alias: assign
+        workers-auto-discovery:
+          packages: com.component.temporal.assign
+        workers:
+          - task-queue: global
+      - namespace: unassign
+        alias: unassign
+        workers-auto-discovery:
+          packages: com.component.temporal.unassign
+        workers:
+          - task-queue: global
+```
+
+## Customization
+
+All customization points for the root namespace also exist for the non-root namespaces. To specify for a particular 
+namespace users just need to append the alias/namespace to the bean.
+
+```java
+    // TemporalOptionsCustomizer type beans must start with the namespace/alias you defined and end with function class 
+    // name you want to customizer and concat Customizer as the bean name.
+    @Bean
+    TemporalOptionsCustomizer<WorkflowServiceStubsOptions.Builder> assignWorkflowServiceStubsCustomizer() {
+        return builder -> builder.setKeepAliveTime(Duration.ofHours(1));
+    }
+
+    // Data converter is also supported
+    @Bean
+    DataConverter assignDataConverter() {
+        return DataConverter.getDefaultInstance();
+    }
+```
+
+## Injecting
+
+If you want to autowire different `WorkflowClient` instances from different namespaces, you can use the `@Resource` 
+annotation with the bean name corresponding to the namespace alias + `WorkflowClient`:
+
+```java
+    // temporalWorkflowClient is the primary and rootNamespace bean. 
+    @Resource
+    WorkflowClient workflowClient;
+
+    // Bean name here corresponds to the namespace/alias + Simple Class Name
+    @Resource(name = "assignWorkflowClient")
+    private WorkflowClient assignWorkflowClient;
+
+    @Resource(name = "unassignWorkflowClient")
+    private WorkflowClient unassignWorkflowClient;
+```