Update hacking-on-atom-core.md

[fnsengineering]

⚛👋 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
   • 📈 Are you improving performance? Copy the template from https://bit.ly/atom-perf-pr
   • 📝 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
3. Fill in all sections of the template
4. Click "Create pull request"