add subfolders to clean up docs

[Sarah Gaichas]

Probably minor, but we have a lot of loose images in docs right now. I'd suggest putting them in an image folder if we are keeping them here, or else restructuring to pull from a single images folder for many documents.

the setup block for the visualization rmds already has this line in it

#Image Directory
image.dir <- here::here("image")

so we would just import the images from there.
right now there is an additional line in each codeblock going around this; for example

image.dir <- here::here("docs")

knitr::include_graphics(file.path(image.dir, "MABcondition_2019.jpg"))

[Kimberly Bastille (NOAA Contractor)]

created an images under docs to clean it up