README.md

1. Sign in LINE Developers
2. Create LINE_CHANNEL_SECRET & LINE_CHANNEL_ACCESS_TOKEN
3. Sign in OpenAI API
4. Create OPENAI_API_KEY
5. Sign in AWS Lambda
6. Create layer like this
7. Create function like this
8. Create function URL
9. Visit API Gateway
10. Create API for webhook events sent by LINE
11. Edit Timeout