Add instructions on how to contact the package manager to error message

Author: MatteoPologruto

Diff for: arduino/cores/packagemanager/download.go

@@ -125,7 +125,7 @@ func (pme *Explorer) DownloadToolRelease(tool *cores.ToolRelease, config *downlo
 	if resource == nil {
 		return &arduino.FailedDownloadError{
 			Message: tr("Error downloading tool %s", tool),
-			Cause:   errors.New(tr("no versions available for the current OS"))}
+			Cause:   errors.New(tr("no versions available for the current OS, try contacting %s", tool.Tool.Package.Email))}
 	}
 	return resource.Download(pme.DownloadDir, config, tool.String(), progressCB, "")
 }

Diff for: arduino/cores/packagemanager/install_uninstall.go

@@ -313,7 +313,8 @@ func (pme *Explorer) InstallTool(toolRelease *cores.ToolRelease, taskCB rpc.Task
 
 	toolResource := toolRelease.GetCompatibleFlavour()
 	if toolResource == nil {
-		return fmt.Errorf(tr("no compatible version of %s tools found for the current os"), toolRelease.Tool.Name)
+		return fmt.Errorf(tr("no compatible version of %s tools found for the current os, try contacting %s"),
+			toolRelease.Tool.Name, toolRelease.Tool.Package.Email)
 	}
 	destDir := pme.PackagesDir.Join(
 		toolRelease.Tool.Package.Name,