Adding the "Fixing DS mode" section into the "Region Changing" guide

[GabubuAvailable]

Description Heyo. I came here in order to help you and every people who plans to fully region change the console to another region. The reason of doing this PR is because it's missing the DS mode part. You see, When you try to update the network settings on DS mode from the System Settings, or try to load TWiLight Menu++ or a regular DS game, it crashes and gives you this error shown here:

So what I've added in the "Region Changing" guide will cover that part too. For fixing that, TWLFix-CFW by MechanicalDragon0687 is required in order to make the DS mode work properly and play DS games on the 3DS/2DS:

If you have any questions or sugestions on how can I make it better, let me know and we'll find a solution!

Thank you, Gabubu