You can author your README using Visual Studio Code. Here are some useful editor keyboard shortcuts:

• Split the editor (Cmd+\ on OSX or Ctrl+\ on Windows and Linux)
• Toggle preview (Shift+CMD+V on OSX or Shift+Ctrl+V on Windows and Linux)
• Press Ctrl+Space (Windows, Linux) or Cmd+Space (OSX) to see a list of Markdown snippets

• Visual Studio Code's Markdown Support
• Markdown Syntax Reference

Enjoy!