Hi, while the 0.4.13 textures are freely-licensed you still need to comply with that license. CC BY-SA requires you to credit the original authors of the textures when redistributing them, so please add a LICENSE or README file to this package crediting them. If you go through an 0.4.13 copy of minetest_game you should be able to find all the credits in the README.txt file of each mod.
the terms of the license(cc-by-sa 3.0) https://creativecommons.org/licenses/by-sa/3.0/ require that the license be included in the package. simple way to do that is to make a license.txt file and paste the license in there.
No, you appear to have added a copy of the MIT license for some reason, despite your pack being listed as CC BY-SA 3.0 here... and why the line about Stu specifically at the end, wouldn't it make sense to list everyone in that case? Did you just copy this from some other project?
Now that I have a spare moment, let me give you more specific directions. This is something everyone has to learn at some point, so don't worry if you haven't done it before! (Although please note: I am not a lawyer)
The license the textures use, CC BY-SA 3.0, is mainly about attribution and keeping the license intact when making derivatives. You can find a complete description of the license and what it requires here
Attribution is defined in section 4(c). Here's a simpler version of what the license asks you to provide:
❌ All existing copyright notices -- You don't have this but you can probably find them where you sourced the textures, maybe in LICENSE files if supplied?
☑️ The name of the author -- You have this in your README file
❌ The title of the work if provided (In this case, the name of the mod / TP the files are from) -- You have this for some textures in your README file, but not everything. You can probably complete this by specifying that the textures are from Minetest Game, unless there are others I've missed.
❌ A URL to the license -- This, with the copyright notices, would go in your LICENSE file.
☑️ Credit to the authors, along with any modifications made -- I think your README covers this unless you made edits and didn't note those there?
In most LICENSE files you'll see copyright notices (ie. "Copyright (c) <year><name>") next to the files, followed by the text of the license. In the case of this license, you provide a link instead of the full text. Creative Commons offers text blurbs that you can use for this, the one for CC BY-SA 3.0 is here.
Hopefully you have a better idea of what's missing now, and how to find that info. If any other approvers want to jump in and correct the above, please feel free to do so.