Create SECURITY.md

[geogekuo]

⚛👋 Hello there! Welcome. Please follow the steps below to tell us about your contribution.

1. Copy the correct template for your contribution

• 🐛 Are you fixing a bug? Copy the template from https://bit.ly/atom-bugfix-pr
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• 📝 Are you updating documentation? Copy the template from https://bit.ly/atom-docs-pr
• 💻 Are you changing functionality? Copy the template from https://bit.ly/atom-behavior-pr

2. Replace this text with the contents of the template
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