docs(operators): add documentation for last
docs(operators): add documentation for last

add documentation and an example for the last operator

close #94

ashwin-sureshkumar/rxjs-docs,ashwin-sureshkumar/rxjs-docs,ashwin-sureshkumar/rxjs-docs,ReactiveX/rxjs-docs,ReactiveX/rxjs-docs,ReactiveX/rxjs-docs