Add dvue user presentation documentation

- Introduced a comprehensive markdown file for the dvue user presentation.
- Included sections on the purpose of dvue, its features, agenda, and detailed explanations of workflows.
- Documented the interactive map, data selection, plotting, transforms, and derived series functionalities.
- Added examples and use cases to illustrate the capabilities of dvue.
- Provided a demo section with step-by-step instructions for showcasing dvue features.

Author: dwr-psandhu