nasm: add license

see issue #43716

pkgs/development/compilers/nasm/default.nix

···
     description = "An 80x86 and x86-64 assembler designed for portability and modularity";
     platforms = platforms.unix;
     maintainers = with maintainers; [ pSub willibutz ];
+    license = licenses.bsd2;
   };
 }