Completed: added translation for docs

[tanapl]

1. added English translation files:

• contract_en.md
• deploy_en.md
• devenv_mac_en.md

2. changed docs files' name:

• contract.md -> contract_jp.md
• deploy.md -> deploy_jp.md
• devenv_mac.md -> devenv_mac_jp.md

3. fixed files:

• deploy_jp.md
• devenv_mac_jp.md
• README.md

[vercel[bot]]

@tanapl is attempting to deploy a commit to the Code for Japan Team on Vercel.

A member of the Team first needs to authorize it.