DOC: add docs to grade service
DOC: add docs to grade service

alexcu/doubtfire-web,doubtfire-lms/doubtfire-web,final-year-project/doubtfire-web,doubtfire-lms/doubtfire-web,doubtfire-lms/doubtfire-web,doubtfire-lms/doubtfire-web,final-year-project/doubtfire-web,alexcu/doubtfire-web