supplement PR submission process

CONTRIBUTING.md

@@ -124,6 +124,7 @@ When reporting issues, refer to this format:
 - Raise your idea as an *issue* on [GitHub](https://github.com/mindspore-ai/mindspore/issues) or [Gitee](https://gitee.com/mindspore/mindspore/issues)
 - If it is a new feature that needs lots of design details, a design proposal should also be submitted.
 - After reaching consensus in the issue discussions and design proposal reviews, complete the development on the forked repo and submit a PR.
+- After submitting the PR, you need to sign the CLA, check the code according to the checklist, and comment */retest* to run the code check.
 - None of PRs is permitted until it receives **2+ LGTM** from approvers. Please NOTICE that approver is NOT allowed to add *LGTM* on his own PR.
 - After PR is sufficiently discussed, it will get merged, abandoned or rejected depending on the outcome of the discussion.
 

CONTRIBUTING_CN.md

@@ -123,6 +123,7 @@
 
 - 在 [GitHub](https://github.com/mindspore-ai/mindspore/issues) 或者 [Gitee](https://gitee.com/mindspore/mindspore/issues) 针对一个*issue*提出你的解决方案。
 - 在议题讨论和设计方案审核达成共识后，fork后完成开发后提交PR
+- 提交PR后需要：签订cla，根据自检列表完成代码自检，在评论区评论/retest运行代码检查
 - 贡献者的代码需要至少两个committer*LGTM*，PR才可以被允许推送，注意贡献者不允许在自己的PR上添加*LGTM*。
 - 在PR被详细评审后，这个PR将会被确定能否被合入。