推奨ディレクトリ構成
<myproduct>
├── go.mod
├── go.sum
├── <env.go> <- package <myproduct>
├── <github.go> <- package <myproduct>
├── <slack.go> <- package <myproduct>
├── <myapp-1>
│ └── main.go <- package main
└── <myapp-2>
└── main.go <- package main