modify the readme for keyvault certificates sample (Azure#18411)

Author: zhichengliu12581

sdk/spring/azure-spring-boot-samples/azure-spring-boot-sample-keyvault-certificates/README.md

@@ -1,14 +1,29 @@
 # Azure Spring Boot Key Vault Certificates client library for Java
+
 ## Key concepts
+This sample illustrates how to use [Azure Spring Boot Starter Key Vault Certificates ][azure_spring_boot_starter_key_vault_certificates].
+
+In this sample, a certificate named `self-signed` is stored into an Azure Key Vault, and a sample Spring application will use its value as a configuration property value.
+
 ## Getting started
 
 ### Environment checklist
 We need to ensure that this [environment checklist][ready-to-run-checklist] is completed before the run.
 
+### Store Certificate
+We need to store certificate `self-signed` into Azure Key Vault with the following steps: [store certificate ][steps_to_store_certificate]
+
 ## Examples
 ## Troubleshooting
 ## Next steps
+## Run with Maven
+```
+cd azure-spring-boot-samples/azure-spring-boot-sample-keyvault-certificates
+mvn spring-boot:run
+```
 ## Contributing
 
 <!-- LINKS -->
 [ready-to-run-checklist]: https://github.com/Azure/azure-sdk-for-java/blob/master/sdk/spring/azure-spring-boot-samples/README.md#ready-to-run-checklist
+[azure_spring_boot_starter_key_vault_certificates]: https://github.com/Azure/azure-sdk-for-java/blob/master/sdk/spring/azure-spring-boot-starter-keyvault-certificates/README.md
+[steps_to_store_certificate]: https://github.com/Azure/azure-sdk-for-java/blob/master/sdk/spring/azure-spring-boot-starter-keyvault-certificates/README.md#creating-an-azure-key-vault