docs: refine render-function (#903)
docs: refine render-function (#903)

* docs: refine render-function

* Update src/v2/guide/render-function.md

* Apply suggestions from code review

Co-Authored-By: Justineo <0af221f268e7c2f9e57d4dacd37636a2f4fed93a@gmail.com>

vuejs/cn.vuejs.org,vuejs/cn.vuejs.org