Add link to ServiceStack v3 in Usage quota's exception message

Author: mythz

src/ServiceStack.Text/LicenseUtils.cs

@@ -103,7 +103,7 @@ static LicenseUtils()
 
         public static class ErrorMessages
         {
-            private const string UpgradeInstructions = " Please see https://servicestack.net to upgrade to a commercial license.";
+            private const string UpgradeInstructions = " Please see https://servicestack.net to upgrade to a commercial license or visit https://github.com/ServiceStackV3/ServiceStackV3 to revert back to the free ServiceStack v3.";
             internal const string ExceededTextTypes = "The free-quota limit on '{0} ServiceStack.Text Types' has been reached." + UpgradeInstructions;
             internal const string ExceededRedisTypes = "The free-quota limit on '{0} Redis Types' has been reached." + UpgradeInstructions;
             internal const string ExceededRedisRequests = "The free-quota limit on '{0} Redis requests per hour' has been reached." + UpgradeInstructions;