add pr template

.github/PULL_REQUEST_TEMPLATE.md

+### Summary of this Pull Request (PR) 拉取请求的简述  
+
+**Add description here.**  
+
+### Intent for your PR 拉取请求的目的  
+
+Choose one (Mandatory):  
+
+- [ ] This PR is for a code-review and is intended to get feedback 本拉取请求是一个草稿版本  
+- [ ] This PR is mature, and ready to be integrated into the repo 本拉取请求是一个成熟版本  
+
+### Reviewers (Mandatory): 代码审阅者（必须指定）
+(@<github.com username(s)> Ex: @user1, @user2)  
+
+
+### Code Quality： 代码质量  
+As part of this pull request, I've considered the following:  
+我在这个拉取请求中考虑了：
+- [ ] Style guide is adhered to, including spacing, naming and other style 代码的格式正确  
+- [ ] All redundant code is removed and cleaned up 没有垃圾代码
+- [ ] All modifications are justified 所有变更均有原因  
+- [ ] I've commented appropriately where code is tricky 难懂代码均被注释  
+- [ ] Code in this PR is of high quality 本拉取请求高质量  
+
+### Testing：代码测试
+
+I've tested the code using the following test programs (provide list here):  
+我已经在如下用例上跑过测试：  
+
+- [ ] application 1
+- [ ] application 2
+- [ ] ...(add others here)