Add Powershell Installation Instructions for Copilot (#52141)

* Add Powershell Installation Instructions for Copilot

* Edit PowerShell URL and generalize instructions

Co-authored-by: Jesse Squire <[email protected]>

---------

Co-authored-by: Jesse Squire <[email protected]>

Author: JennyPng

.github/copilot-instructions.md

@@ -2,6 +2,9 @@
 
 This repo contains Azure SDKs for various Azure services and tools that generate them.
 
+## Prerequisites
+- To use MCP tool calls, PowerShell must be installed. Provide [PowerShell installation instructions](https://learn.microsoft.com/powershell/scripting/install/installing-powershell) if not installed, and recommend restarting the IDE to use the MCP server.
+
 ## Folder Structure
 
 - `/eng/packages/http-client-csharp`: Contains the source code of the generator for Azure Data Plane SDKs (aka Azure Generator).