add comment on CONTRIBUTING

CONTRIBUTING-en.md

@@ -8,7 +8,9 @@ Direct push is not allowed for creating a new module. And you should support `Gi
 For the first time, please submit by PR, you can obtain the permission of collaborator after this PR is merged.
 * Everyone creates a new one in their own package named `packageName.md` in sub module, add the index and then link it to the current sub module README.md, refer to `python-leetcode`.
 
-this is a python sub module, if you want to create a new module that the language you use is not exists you should look at this structure.
+> After obtaining the permission of collaborator, please use `git push` cautiously. Before each push, first pull the latest remote code and resolve the conflict locally (be sure to keep others' commit well in case of conflict).
+
+This is a python sub module, if you want to create a new module that the language you use is not exists you should look at this structure.
 
 ```
 python-leetcode

CONTRIBUTING.md

@@ -8,6 +8,8 @@
 - 在子模块下每个人为自己建一个package，用以区分不同人。第一次以PR形式提交，merge后你将获得Collaborator权限
 - 在子模块下每个人在自己package中新建一个`packageName.md`，增加题目索引再链接到当前项目的README.md
 
+> 获得Collaborator权限后，请谨慎使用`git push`，每次push之前，首先拉取远程最新代码，在本地解决冲突（冲突时一定要将别人的提交保留好）。
+
 如果你要创建新的语言的子模块，应该以下面的python-leetcode项目为例
 
 ```