Merge pull request #3436 from Unity-Technologies/new-pr-template

Adding a new pr template

.github/PR_TEMPLATE/PULL_REQUEST_TEMPLATE.md

+### Proposed change(s)
+
+Describe the changes made in this PR.
+
+### Useful links (Github issues, JIRA tickets, ML-Agents forum threads etc.)
+
+
+
+### Types of change(s)
+
+- [ ] Bug fix
+- [ ] New feature
+- [ ] Code refactor
+- [ ] Breaking change
+- [ ] Documentation update
+- [ ] Other (please describe)
+
+### Checklist
+- [ ] I have added tests that prove my fix is effective or that my feature works
+- [ ] I have added updated the changelog (if applicable)
+- [ ] I have added necessary documentation (if applicable)
+- [ ] I have updated the migration guide (if applicable)
+
+### Other comments