docs(README): Add method to calendar in quickstart example

[Justin-Koningsberger]

About this Pull Request

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  • Updates the README to include a method in the calendar object, so outlook displays the invitation properly. Without it there are no accept/decline buttons shown, and the filename is "calendar not supported message.ics".
• What is the current behavior? (You can also link to an open issue here)
  • …
• What is the new behavior (if this is a feature change)?
  • …
• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
  • No

• Other information:

Pull Request Checklist

• My code follows the code style of this project
  • Run npm run lint to double check
• My change requires a change to the documentation
  • I have updated the documentation accordingly
• I have added tests to cover my changes
  • Run npm run test to run the unit tests and npm run coverage to generate a coverage report
• All new and existing tests passed
• My commit messages follow the commit guidelines

[sebbo2002]

🎉 This PR is included in version 6.0.1-develop.1 🎉

The release is available on:

• npm package (@next dist-tag)
• GitHub release
• v6.0.1-develop.1

Your semantic-release bot 📦🚀

[sebbo2002]

🎉 This PR is included in version 6.0.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release
• v6.0.1

Your semantic-release bot 📦🚀