docs: add pull request template

[ChanJoon]

Description

New PR Template

Motivation and Context

This is example content of this template.

References

• stevemao/github-issue-templates
• angular/angular

How has this been tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Documentation content changes
• Other... Please describe:

This PR doesn't include any code changes or documentation update.

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

After this PR merged, README.md should be updated.

[ChanJoon]

@movie5 머징 부탁드립니다