Add a description for time pattern trigger

[karwosts]

Proposed change

Add a description for time pattern trigger in the automation editor. Examples:

• "Trigger on the 12th hour" (hours: 12)
• "Trigger every second of every minute of every hour" (seconds: *)
• "Trigger every minute of every hour" (minutes: *)
• "Trigger every second of the 0th minute of the 12th hour" (seconds: *, hours: 12)
• "Trigger every 3 minutes of every hour" (minutes: /3)
• "Trigger on the 3rd second of the 7th minute of the 21st hour" (hours: 21, minutes: 7, seconds: 3)
• "Trigger every 5 seconds of every minute of the 0th hour" (hours: 0, minutes: *: seconds: /5)
• "Trigger every 30 seconds of every 20 minutes of every 3 hours" (hours: /3, minutes: /20: seconds: /30)

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New feature (thank you!)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Example configuration

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue or discussion:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• There is no commented out code in this PR.
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io