Putting the license xml file in the root, and marking it as Content should work.
Consider using LicenseHelper class at startup to check if the license is valid:
LicenseStatus status = LicenseHelper.GetLicenseStatus();
string fileName = LicenseHelper.GetLicensePath();
if (status != LicenseStatus.Valid)
{
throw new Exception(
string.Format("License is not valid: '{0}'. Loaded from '{1}'.",
status,
fileName));
}