message: API: Add ExportController docs
diff: @@ -48,6 +48,9 @@ export class ExportController {
  * }],
  * "hasAccessKey": false
  * }
  + *
  + * @apiError NotFoundError If the course couldn't be found.
  + * @apiError ForbiddenError assertUserExportAuthorization check.
  */
  @Get('/course/:id')
  async exportCourse(@Param('id') id: string, @CurrentUser() currentUser: IUser) {
  @@ -76,6 +79,9 @@ export class ExportController {
  * "description": "Some lecture desc",
  * "units": []
  * }
  + *
  + * @apiError NotFoundError If the lecture couldn't be found.
  + * @apiError ForbiddenError assertUserExportAuthorization check.
  */
  @Get('/lecture/:id')
  async exportLecture(@Param('id') id: string, @CurrentUser() currentUser: IUser) {
  @@ -108,6 +114,9 @@ export class ExportController {
  * "markdown": "Welcome, this is the start",
  * "__t": "free-text"
  * }
  + *
  + * @apiError NotFoundError If the unit couldn't be found.
  + * @apiError ForbiddenError assertUserExportAuthorization check.
  */
  @Get('/unit/:id')
  async exportUnit(@Param('id') id: string, @CurrentUser() currentUser: IUser) {
  