Description tab in vis spy

[fbaligand]

On the spy part of a visualization, it would be nice to add a tab named "Documentation" (or "Description") containing information about this visualization.
This information would be editable (using MarkDown for example).

This would allow the ability to add self-documentation for a visualization.
The visualization maker set this documentation, and the visualization user is happy to read this documentation to understand well what this visualization is for.

[rashidkpc]

IIRC description is an existing part of the schema for saved objects that we don't currently expose. It would be pretty easy to drop that into the spy.

[fbaligand]

This would be great !

[nreese]

closing - duplicate of #2538