!6231 【轻量级 PR】：update .github/PULL_REQUEST_TEMPLATE.md.

Merge pull request !6231 from Simson/N/A

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,6 +1,8 @@
 <!--  Thanks for sending a pull request!  Here are some tips for you:
 
-If this is your first time, please read our contributor guidelines: https://github.com/mindspore-ai/mindspore/blob/master/CONTRIBUTING.md
+1) If this is your first time, please read our contributor guidelines: https://github.com/mindspore-ai/mindspore/blob/master/CONTRIBUTING.md
+
+2) If you want to contribute your code but don't know who will review and merge, please add label `mindspore-assistant` to the pull request, we will find and do it as soon as possible.
 -->
 
 **What type of PR is this?**