```ruby
# Be sure to restart your server when you modify this file.

# Add new mime types for use in respond_to blocks:
# Mime::Type.register "text/richtext", :rtf
```

Add :xls and :csv as custom mime type
user
```ruby
# Be sure to restart your server when you modify this file.

# Add new mime types for use in respond_to blocks:
# Mime::Type.register "text/richtext", :rtf
Mime::Type.register 'application/xls', :xls
Mime::Type.register 'text/csv', :csv
```
assistant