Sprockets::Rails::Helper::AssetNotPrecompiled in Welcome#index

[Ian Einser]

Hello, i got a problem here. I got this error message when i run http://localhost:3000

Asset was not declared to be precompiled in production.
Add Rails.application.config.assets.precompile += %w( html5.js ) to config/initializers/assets.rb and restart your server

i try to locate assets.rb but couldn't find it. Any idea? Thanks