code: def add_comment(self, request, project, work_item_id):
          
          route_values = {}
          if project is not None:
              route_values['project'] = self._serialize.url('project', project, 'str')
          if work_item_id is not None:
              route_values['workItemId'] = self._serialize.url('work_item_id', work_item_id, 'int')
          content = self._serialize.body(request, 'WorkItemCommentCreateRequest')
          response = self._send(http_method='POST',
                                location_id='608aac0a-32e1-4493-a863-b9cf4566d257',
                                version='5.1-preview.1',
                                route_values=route_values,
                                content=content)
          return self._deserialize('WorkItemCommentResponse', response)
docs: AddComment.
          [Preview API] Add a comment on a work item.
          :param :class:`<WorkItemCommentCreateRequest> <azure.devops.v5_1.work_item_tracking_comments.models.WorkItemCommentCreateRequest>` request: Comment create request.
          :param str project: Project ID or project name
          :param int work_item_id: Id of a work item.
          :rtype: :class:`<WorkItemCommentResponse> <azure.devops.v5_1.work-item-tracking-comments.models.WorkItemCommentResponse>`