For the file name, take the name of the original texture without the extension and add it to the beginning of .texture_set.json, for instance, gold_ore.texture_set.json, for the gold_ore.png. Then the JSON file goes into the same folder.
For the file name, take the name of the original texture without the extension and add it to the beginning of .texture_set.json, for instance, gold_ore.texture_set.json, for the gold_ore.png. Then the JSON file goes into the same folder.