adding use cases to FathomNet

[kakanikatija]

add "new" challenges to root directory with links to benchmarks

[kakanikatija]

FathomNet: high-level summary of popular use cases

topics:

• object detector without class output
• midwater vs. benthic images
• vulnerable marine ecosystems
• same same but different (siamese model)
• midwater transects
• benthic transects
• distribution shifts

[hohonuuli]

Perhaps add this content to the "About Us" page

[kevinsbarnard]

Link to competitions as well.

Better suited for blog.