🤖 docs: add Windows installation instructions

Author: deansheather

docs/install.md

@@ -8,6 +8,7 @@ Download pre-built binaries from [the releases page](https://github.com/coder/mu
 
 - **macOS**: Signed and notarized DMG (separate builds for Intel/Apple Silicon)
 - **Linux**: AppImage
+- **Windows**: Installer exe
 
 ### Development Builds
 
@@ -17,6 +18,8 @@ Down pre-built binaries of `main` from [GitHub Actions](https://github.com/coder
   - `macos-dmg-x64` (Intel Macs)
   - `macos-dmg-arm64` (Apple Silicon)
 - **Linux**: AppImage (portable, works on most distros)
+- **Windows**: Installer exe
+  - `windows-installer-x64`
 
 To download:
 
@@ -44,6 +47,13 @@ The app is code-signed and notarized by Apple, so it will open without security
 2. Make it executable: `chmod +x Mux-*.AppImage`
 3. Run it: `./Mux-*.AppImage`
 
+**Windows:**
+
+1. Download the installer exe (`windows-installer-x64`)
+2. Run the installer
+3. Follow the installation prompts
+4. Launch Mux from the Start menu or desktop shortcut
+
 ### Testing Pre-Release Builds
 
 ⚠️ **Note**: Only builds from the `main` branch are signed and notarized. If you're testing a build from a pull request or other branch, you'll need to bypass macOS Gatekeeper: