Adding Article on model_fcn_resnet

[DerrickUnleashed]

This PR adds user stories for draw_segmentation_masks() vision_make_grid() and model_fcn_resnet50()

[DerrickUnleashed]

@cregouby, I can add more examples like using model_fcn_resnet101() and drawing masks for each image separately. Would you like us to implement that, or are the examples given?

Also, can we make the name of the file more descriptive, or is it fine?

[cregouby]

Hello @DerrickUnleashed,

This is not the vignette but a article. It is nice, so I keep it, and I will review it.

But for me, we didn't fix #113. In order to fix #113, we have be as educative and informative as the python vision vignette, i.e. to copy the markdown text, and just replace the code (by hopefully much simpler and readable code chunks)

Please initialize the vignette with usethis::use_vignette("visualization_utils", title = "Visualization utilities" )