more detail on how to refer to a calendar

[cburgdorfer]

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Proposed changes

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the mailing list/slack team.
• I have run grunt to verify the unit tests pass
• [n/a] I have added suitable unit tests to cover the new/changed functionality

[jsf-clabot]

All committers have signed the CLA.

[coveralls]

Coverage remained the same at 72.285% when pulling ffb0041 on cburgdorfer:patch-2 into 0c4bfdd on node-red:master.

[dceejay]

Hi - you have raised two Pull requests with the same title - and neither has a brief description of what that are trying to fix or improve. Can you add some more info and delete/close the one you don't want ? Thanks

[cburgdorfer]

I will make a new pull request. Apologies for the confusion.