feat(nix): add nix build

tools/fetch_spotiflac_backend.sh

@@ -6,7 +6,7 @@ FOLDER=lib
 
 rm -rf lib/
 git clone https://github.com/afkarxyz/SpotiFLAC.git
-mv SpotiFLAC/backend/ lib/
+cp -r SpotiFLAC/backend/ lib/
 mkdir -p app/ 
 cp SpotiFLAC/app.go app/app.go
 rm -rf SpotiFLAC
@@ -14,6 +14,9 @@ rm -rf SpotiFLAC
 sed -i "s/package main/package app/g" app/app.go
 sed -i "s/\"spotiflac\/backend\"/backend \"github.com\/Superredstone\/spotiflac-cli\/lib\"/g" app/app.go
 
+# Nix shenanigans
+chmod -R 777 lib
+
 for i in $(ls lib/); do
 	sed -i "s/package backend/package $FOLDER/g" $FOLDER/$i
 done