Update doc for award emoji API

## What does this MR do?

It fixes some docs for the award emoji API.

## Are there points in the code the reviewer needs to double check?

@zj I'm assigning you since you wrote this docs.

## Does this MR meet the acceptance criteria?

~~- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added~~
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)

~~- [ ] API support added~~

~~- Tests~~

~~- [ ] Added for this feature/bug~~

  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5386