Add changelog and readme updates for Linux install support

Co-authored-by: garrytrinder <11563347+garrytrinder@users.noreply.github.com>

Author: Copilot

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added:
 
+- Install: Added automated install and upgrade support for Linux using official setup scripts
 - Quick Fixes: Enable local language model fix now adds or updates `languageModel.enabled: true` for supported plugins only
 
 ### Fixed:

README.md

@@ -11,7 +11,7 @@ Supercharge your [Dev Proxy](https://aka.ms/devproxy) workflow with IntelliSense
 
 ## Quick Start
 
-1. **Install this extension** - [Install from VS Code](vscode:extension/garrytrinder.dev-proxy-toolkit). You'll be prompted to install Dev Proxy if it's not already installed.
+1. **Install this extension** - [Install from VS Code](vscode:extension/garrytrinder.dev-proxy-toolkit). You'll be prompted to install Dev Proxy if it's not already installed. Automated install is supported on Windows (winget), macOS (Homebrew), and Linux (setup script).
 2. **Create a config** - Run `Dev Proxy Toolkit: Create configuration file` from the Command Palette
 3. **Configure your proxy** - Add URLs to watch and plugins using snippets (type `devproxy-`) or let [GitHub Copilot help](#mcp-server)
 4. **Start Dev Proxy** - Run `Dev Proxy Toolkit: Start` from the Command Palette