Update install-vsix-appveyor.ps1

Author: josesimoes

install-vsix-appveyor.ps1

@@ -1,4 +1,9 @@
 $vsixPath = "$($env:USERPROFILE)\nanoFramework.Tools.VS2017.Extension.vsix"
 (New-Object Net.WebClient).DownloadFile('https://marketplace.visualstudio.com/_apis/public/gallery/publishers/vs-publisher-1470366/vsextensions/nanoFrameworkVS2017Extension/0/vspackage', $vsixPath)
 "`"C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\Common7\IDE\VSIXInstaller.exe`" /q /a $vsixPath" | out-file ".\install-vsix.cmd" -Encoding ASCII
-& .\install-vsix.cmd
+
+'Installing nanoFramework VS extension ...' | Write-Host -ForegroundColor White -NoNewline
+
+& .\install-vsix.cmd > $null
+
+'OK' | Write-Host -ForegroundColor Green