学んだこと（railsの復習・MVC） ルーティング get "posts/index" => "posts#index" get "posts/new" => "posts#new" get "posts/:id" => "posts#show" post "posts/create" => "posts#create" 「get "posts/:id" => "posts#show"」→詳細ページに飛ぶ時、URL…