Transition from NUS Downloader to NUSGet

[grunt22fox]

NUS Downloader is the current application referenced in the guide for obtaining resources from NUS. As referenced in another pull request (#149), this program is outdated and depreciated. This PR seeks to transition to NUSGet, a more user friendly and actively maintained application for the same purpose.

TODO:

Change references in bricks.md ✅
Change references in cios.md ✅
Change references in themes.md ✅
Change references in update.md ✅

This PR will additionally update license information for the guide to 2026.

[mpgiii]

Is there any reason we haven't had any more movement on this PR? Would love to get this transition to NUSGet in.

[playerjmr]

ok three things:

1. I noticed that in your pr for nusget you reccomended for windows users to download NUSGet-Windows-x86_64-onefile-bin.zip but as a windows user myself i've had less antivirus issues if I use the NUSGet-Windows-x86_64-bin.zip instead, I would be more comfortable if that was recommended to use instead.
2. In the cios section, the wads need to be named a specific way and it doesnt say anywhere in the guide to rename the files. For example, IOS 38 is downloaded as IOS-38-v4123-Wii.wad when it needs to be IOS38-64-v4123.wad otherwise the d2x cios installer cannot find it.
3. In the themes page under the Wii via nusget tab, it mentions nusget.exe, which should be changed like it is elsewhere to "in the same directory as your NUSGet executable." ill make a suggestion below so you know what im talking about. other than that, once I see these changes reflected plus the above suggestions from @JohnVeness committed then it should be ready to merge.