docs: Update label-studio-ml-backend docs (#6258)

Co-authored-by: farioas <farioas@users.noreply.github.com>
Co-authored-by: makseq <makseq@users.noreply.github.com>
Co-authored-by: micaelakaplan <micaelakaplan@users.noreply.github.com>
Co-authored-by: Caitlin Wheeless <caitlin.wheeless@gmail.com>