Feat: Adds tutorial on how to include images from unDraw/DrawKit

[vibalre]

Have you read the Contributing Guidelines?

Closes #23

Changes description

• Adds vignette on how to use images in for empty state content.

[rszymanski]

Suggestion: What do you think about updating the README example with the gif we use in the tutorial?

[rszymanski]

Requested Change:

The vignette doesn't show in the pkgdown site:

I see we are using some customization in pkgdown - perhaps we can reuse the setup from shiny.router - @jakubnowicki is probably the best person to ask about this ;)

[jakubnowicki]

Requested Change:

The vignette doesn't show in the pkgdown site:

I see we are using some customization in pkgdown - perhaps we can reuse the setup from shiny.router - @jakubnowicki is probably the best person to ask about this ;)

Since this is just a single tutorial, I suggest something similar to shiny.benchmark: https://github.com/Appsilon/shiny.benchmark/blob/main/pkgdown/_pkgdown.yml#L38