Move and edit the pull request template

Author: LukasFehring

.github/PULL_REQUEST_TEMPLATE/pull-request-template.md

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+> Thanks for contributing a pull request! Please ensure you have taken a look at the contribution guidelines: https://github.com/automl/SMAC3/blob/main/CONTRIBUTING.md
+
+#### Reference Issues/PRs
+> Example: Fixes #1234. See also #3456.
+> Please use keywords (e.g., Fixes) to create link to the issues or pull requests you resolved, so that they will automatically be closed when your pull request is merged. See https://github.com/blog/1506-closing-issues-via-pull-requests
+
+#### Description, Motivation and Context
+> Provide a short description of your changes.
+
+#### Changes
+> Explain your changes in detail here.
+
+#### Type Of Changes
+> What types of changes does your code introduce? Put an `x` in all the boxes that apply:
+- [ ] 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)
+
+#### What is Missing?
+> Please provide any further information that is needed to close this PR.
+> This could be another PR that is blocking this PR, or any further changes
+> that need to be addressed in the future.
+
+#### Checklist
+> Go over all the following points, and put an `x` in all the boxes that apply.
+> Should there be a good argument to differ, please provide a reasoned explanation.
+- [ ] My change is based on the latest stage of the `develop` branch.
+- [ ] My change required a change of the documentation, which has been done.
+- [ ] I checked that the documentation can be build, visualizes everything as expected, and does not contain any warnings.
+- [ ] I have added/adapted tests to cover my changes.
+- [ ] The tests can be executed successfully.
+- [ ] I have added a description of the changes to `CHANGELOG.rst`.
+
+#### Any other comments?
+
+> We appreciate your effort, but please be aware that we are not working full-time on this project. We welcome any contribution and value your effort, no matter how minor they are. If we are slow to review, either the pull request needs some benchmarking, tinkering, convincing, etc. or more likely the reviewers are simply busy. In either case, we ask for your understanding during the review process.
+> 
+> Thanks for contributing!