当我运行时rails generate paperclip user avatar，我得到了这个错误
创建 db/migrate/20130806042409_add_attachment_avatar_to_users.rb /home/.../.rvm/gems/ruby-1.9.3-p448/gems/thor-0.18.1/lib/thor/actions/create_file.rb:63:in `初始化'：权限被拒绝 - /home/tairy/Documents/sheqwang/db/migrate/20130806042409_add_attachment_avatar_to_users.rb (Errno::EACCES)