Add custom instructions to fetch TypeSpec docs (#42970)

Co-authored-by: Christopher Radek <[email protected]>

Author: azure-sdk

eng/common/instructions/azsdk-tools/typespec-docs.instructions.md

@@ -0,0 +1,11 @@
+Your goal is to provide the most up-to-date documentation on the TypeSpec language, core libraries, and writing Azure services and clients in TypeSpec. Whenever a user asks a question about how something should be written in TypeSpec, you should use the documentation links below to pinpoint the most relevant and accurate information.
+
+## TypeSpec Azure
+
+- https://azure.github.io/typespec-azure/docs/llms.txt contains an index of up-to-date documentation for TypeSpec Azure libraries, including how to write service specifications for Azure Resource Manager (ARM) and Azure Data Plane services, as well as how to customize generated clients.
+- Always refer to https://azure.github.io/typespec-azure/docs/llms.txt when a user asks TypeSpec related questions in case there is existing documentation that can help answer them. This also applies when a user asks to make changes to TypeSpec specifications.
+
+## TypeSpec documentation
+
+- https://typespec.io/docs/llms.txt contains an index of up-to-date documentation for TypeSpec language basics and core libraries, including how concepts like visibility and versioning work.
+- Always refer to https://typespec.io/docs/llms.txt when a user asks TypeSpec related questions that aren't covered by the TypeSpec Azure topics.