Document ways to use obsidian for d&d

References:
- [Getting Started with Obsidian for D&D](https://www.phd20.com/2021-12-20-getting-started-with-obsidian-dnd/)
- [Obsidian Fantasy Calendar](https://github.com/fantasycalendar/obsidian-fantasy-calendar
	- Calendars from [Fantasy Calendar App](https://app.fantasy-calendar.com/calendars)