adding introduction section

Author: NingKuang

articles/virtual-machines/linux/instance-metadata-service.md

@@ -15,8 +15,6 @@ ms.reviewer: azmetadata
 
 # Azure Instance Metadata service
 
-## Summary
-
 The Azure Instance Metadata Service (IMDS) provides information about currently running virtual machine instances and can be used to manage and configure your virtual machines.
 This includes the SKU, storage, network configurations, and upcoming maintenance events. For a complete list of the data that is available, see [metadata APIs](#metadata-apis). 
 Instance Metadata Service is available for both the VM and virtual machine scale set Instances. It is only available for running VMs created/managed using [Azure Resource Manager](https://docs.microsoft.com/rest/api/resources/). 
@@ -673,7 +671,7 @@ Nonce is an optional 10-digit string. If not provided, IMDS returns the current
 }
 ```
 
-The signature blob is a [pkcs7](https://aka.ms/pkcs7) signed version of document. It contains the certificate used for signing along with the VM details like vmId, sku, nonce, subscriptionId, timeStamp for creation and expiry of the document and the plan information about the image. The plan information is only populated for Azure Market place images. The certificate can be extracted from the response and used to validate that the response is valid and is coming from Azure.
+The signature blob is a [pkcs7](https://aka.ms/pkcs7) signed version of document. It contains the certificate used for signing along with the VM details like vmId, sku, nonce, subscriptionId, timeStamp for creation and expiry of the document and the plan information about the image. The plan information is only populated for Azure Marketplace images. The certificate can be extracted from the response and used to validate that the response is valid and is coming from Azure.
 
 ### Sample 2: Validating that the VM is running in Azure