I should probably make better instructions tbh I haven't thought about it in a while sorry
1) Once you download the file, you can place the zip file directly in the [dwarf fortress install directory(where the games .exe file is)/raw/objects folder and extract all. It should create a bunch of new text files in the raw/objects and raw/objects/text folders, and one new folder with a couple more files in it; a readme and a "list of spells" file and a entity_default.txt file.
Note; if when you extract the zip file, your file program creates a new folder inside raw/objects like raw/objects/"spellcrafts_x" and places all the creature_spellcrafts_x and interaction_spellcrafts_x files inside it along with the folder containing the readmes and the text folder, then you will have to cut and paste everything in that folder out into raw/objects, so that the mods' files are alongside the other game raw files and the "text" folder from the mod merges with the games' own text folder.
2a) If you don't have any other mods or you're sure your other mods don't make any changes to the entity_default.txt file, you can just copy-paste the entity_default.txt file in the new folder into raw/objects itself and overwrite the original when it asks. Then just delete or move out of the raw/objects folder the extra files folder and zip file, and generate a new world and you're done.
2b) If you do have other mods installed, you can open the readme.txt file, and inside is a block of code that should start with [permitted_job:alchemist]. Select that and everything below it down to where it returns to normal English text, and copy it. Then go back into raw/objects itself (not the subfolder) and open entity_default.txt, and under where it says entity:mountain, scroll down a few dozen lines, and paste in that block of code. Then hold ctrl-f and search for entity:plains, and under that again scroll down and paste in that block of text. That should be enough to let dwarves and human civs in-game sell you magic potions and let you make your own. If your other mods add more entity_x files (spellcrafts adds to entity_magicians) you can also go into entities they add and give them the same code. Then delete/move out of the raw/objects folder the extra files folder and zip file, and generate a new world.
2c) If you have another big mod installed and entity_default.txt doesnt exist anymore, you will have to consult with that mods author to figure out which entity_x.txt file and entity definition corresponds to their playable race(s) so you can perform step 2b above.
Or ignore the above, I have added a second playable civ that already has the magic reactions and stuff added, in entity_magicians.txt. the entity should always call itself something like a cult or coven or other weird things, and rarely has more than one site on the world map, so it can be identified by that in the entity selection screen.
3) You can safely delete the folder containing the readme and extra files once installation is complete. In fact I would recommend it. I would also delete the zip file or store it elsewhere outside your dwarf fortress game directory.
Let me know if you have any other problems, thank you!