Merge pull request #408 from 01mf02/contributing

Add contribution guidelines

Author: 01mf02

.github/pull_request_template.md

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+Describe your changes here
+
+### Checklist
+
+- [ ] I have read the [contribution guidelines](../CONTRIBUTING.md).

CONTRIBUTING.md

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+# Contribution guidelines
+
+Any contribution must preserve
+quality,
+maintainability, and
+usability of this project.
+
+To ensure this, you must:
+
+- Write a good description:
+  Provide your personal motivation for changes you propose.
+  Your description should aim to be like the documentation:
+  comprehensible, concise, and complete.
+- Respect the values:
+  Changes must adhere to the goals set out in the README, i.e. they must preserve
+  correctness, performance, and simplicity of the code.
+- Keep it minimal:
+  Changes must be minimal to allow others to verify them in reasonable time.
+  The likelihood of a contribution being accepted is inversely proportional to its size.
+- Take your time:
+  Achieving high quality takes time.
+  As a rough guideline,
+  writing new content takes me about 10 to 100 times longer than reading it.
+  The ratio for your changes should be roughly in the same order of magnitude.
+- Document: Document user-observable changes in `docs/`.
+- Test:
+  Add unit or shell tests to the documentation if they might interest users.
+  Include more exotic tests in the test suites of the respective crates.
+- Benchmark:
+  Benchmark performance-critical changes and provide
+  results as well as instructions how to reproduce them.
+
+You must not:
+
+- Duplicate code:
+  Code duplication is a serious problem for long-term project maintenance.
+  Use existing project infrastructure wherever possible, and do not copy-paste.
+- Add dependencies:
+  Dependencies take effort to maintain, in particular to validate and to update.
+  Therefore, new dependencies may only be added in exceptional cases.
+  All dependencies must be compatible with the spirit of this project and
+  add significant value to it.
+- Include machine-generated content:
+  All contributed content, such as description, code, and documentation,
+  must be human-written by the contributor, to ensure its quality.
+
+Thank you for respecting these guidelines!
+I am looking forward to your contributions.