Update Guidelines.md

Added link to ARM guidelines to help avoid confusion for teams who come here when they are implementing ARM APIs.

Author: markweitzel

azure/Guidelines.md

@@ -26,20 +26,17 @@ Please ensure that you add an anchor tag to any new guidelines that you add and
 
 ## Introduction
 
-These guidelines offer prescriptive guidance that Azure service teams MUST follow ensuring that customers have a great experience by designing APIs meeting these goals:
+These guidelines apply to Azure service teams implementing _data plane_ APIs. They offer prescriptive guidance that Azure service teams MUST follow ensuring that customers have a great experience by designing APIs meeting these goals:
 - Developer friendly via consistent patterns & web standards (HTTP, REST, JSON)
 - Efficient & cost-effective
 - Work well with SDKs in many programming languages
 - Customers can create fault-tolerant apps by supporting retries/idempotency/optimistic concurrency
 - Sustainable & versionable via clear API contracts with 2 requirements:
   1. Customer workloads must never break due to a service change
   2. Customers can adopt a version without requiring code changes
+Technology and software is constantly changing and evolving, and as such, this is intended to be a living document. [Open an issue](https://github.com/microsoft/api-guidelines/issues/new/choose) to suggest a change or propose a new idea. Please read the [Considerations for Service Design](./ConsiderationsForServiceDesign.md) for an introduction to the topic of API design for Azure services. *For an existing GA'd service, don't change/break its existing API; instead, leverage these concepts for future APIs while prioritizing consistency within your existing service.*
 
-Technology and software is constantly changing and evolving, and as such, this is intended to be a living document. [Open an issue](https://github.com/microsoft/api-guidelines/issues/new/choose) to suggest a change or propose a new idea.
-
-See the [Considerations for Service Design](./ConsiderationsForServiceDesign.md) for an introduction to the topic of API design for Azure services.
-
-*NOTE: For an existing GA'd service, don't change/break its existing API; instead, leverage these concepts for future APIs while prioritizing consistency within your existing service.*
+*Note: If you are creating a management planen (ARM) API, please refer to the [Azure Resource Manager Resource Provider Contract](https://github.com/Azure/azure-resource-manager-rpc).*
 
 ### Prescriptive Guidance
 This document offers prescriptive guidance labeled as follows: