[.github] add CONTRIBUTING.md

https://docs.github.com/en/communities/setting-up-your-project-for-healthy-contributions/setting-guidelines-for-repository-contributors

.github/PULL_REQUEST_TEMPLATE.md

@@ -40,4 +40,4 @@ The following content must not be changed in the submitted PR message. Otherwise
 - [ ] 所有变更均有原因及合理的，并且不会影响到其他软件组件代码或BSP All modifications are justified and not affect other components or BSP
 - [ ] 对难懂代码均提供对应的注释 I've commented appropriately where code is tricky
 - [ ] 代码是高质量的 Code in this PR is of high quality
-- [ ] 已经使用[formatting](https://github.com/mysterywolf/formatting)等源码格式化工具确保格式符合[RT-Thread代码规范](https://github.com/RT-Thread/rt-thread/blob/master/documentation/contribution_guide/coding_style_cn.md) This PR complies with [RT-Thread code specification](https://github.com/RT-Thread/rt-thread/blob/master/documentation/contribution_guide/coding_style_en.md) 
+- [ ] 已经使用[formatting](https://github.com/mysterywolf/formatting) 等源码格式化工具确保格式符合[RT-Thread代码规范](https://github.com/RT-Thread/rt-thread/blob/master/documentation/contribution_guide/coding_style_cn.md) This PR complies with [RT-Thread code specification](https://github.com/RT-Thread/rt-thread/blob/master/documentation/contribution_guide/coding_style_en.md)