Create pull request template

for coding and code translation

.github/pull_request_template.md

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+> Tip: If this PR is not related to the coding or code translation, please ignore the checklist.
+
+### Checklist
+
+- [] I've tested the code and ensured the outputs are the same as the outputs of reference codes.
+- [] I've checked the codes (formatting, comments, indentation, file header, etc) carefully.
+- [] The code is not relied on a particular environment or IDE and can be runned on a common system (Win, MacOS, Ubuntu).