Update kafka content (#351)
Update kafka content (#351)

* Update kafka content

via
https://github.com/pingcap/docs-cn/pull/513
https://github.com/pingcap/docs-cn/pull/504

* Modify one sentence

* Update wording

* Update wording and format

* Update wording and format

pingcap/docs,pingcap/docs,pingcap/docs