Add Powershell Installation Instructions for Copilot (#46454)

* Add Powershell Installation Instructions for Copilot

* Generalize Instructions

Author: JennyPng

.github/copilot-instructions.md

@@ -22,6 +22,10 @@ The Azure SDK for Java repository contains client libraries for Azure services,
 - **Management Libraries**: Libraries with Maven group `com.azure.resourcemanager`
 - **Spring Libraries**: Libraries with Maven group `com.azure.spring`
 
+### Prerequisites
+
+- To use Azure MCP tool calls, users must have PowerShell installed. Provide [PowerShell installation instructions](https://learn.microsoft.com/powershell/scripting/install/installing-powershell) if not installed, and recommend restarting the IDE to start the MCP server.
+
 ## Behavior
 
 - Always ensure your solutions prioritize clarity, maintainability, and testability.