Add issue template

.github/CONTRIBUTING.md

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+# Contributing
+
+## Issues and bug reports
+When filing a bug report, please state clearly what the problem is, i.e. explain which behaviour is observed and which behaviour is expected instead.
+
+## Development
+Code contributions are much welcomed and appreciated.
+Please make sure that the code is formatted according to the `.clang-format` file in the root of the repository. If you have not configured your editor to format automatically, you can use the [format-code.sh](/scripts/format-code.sh) script or `git clang-format`, before committing.
+
+### Submitting Patches
+You can either submit your changes as a pull request on Github or send them via email to me. In the latter case make sure that your email client does not break the formatting of your patch, I recommend using `git send-email` for this.
+
+### Developer's Certificate of Origin
+By making a contribution to this project, I certify that:
+
+1. The contribution was created in whole or in part by me and I have the right to submit it under the open source license indicated in the file; or
+2. The contribution is based upon previous work that, to the best of my knowledge, is covered under an appropriate open source license and I have the right under that license to submit that work with modifications, whether created in whole or in part by me, under the same open source license (unless I am permitted to submit under a different license), as indicated in the file; or
+3. The contribution was provided directly to me by some other person who certified (1), (2) or (3) and I have not modified it.
+4. I understand and agree that this project and the contribution are public and that a record of the contribution (including all personal information I submit with it, including my sign-off) is maintained indefinitely and may be redistributed consistent with this project or the open source license(s) involved.

.github/ISSUE_TEMPLATE/bug_report.yml

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+name: Guided bug report
+description: "File a bug report. If you know what you are doing, feel free to open a blank issue below."
+body:
+  - type: textarea
+    id: description
+    attributes:
+      label: Describe the bug
+      placeholder: A clear and concise description of what the bug is.
+    validations:
+      required: true
+  - type: textarea
+    id: reproduce
+    attributes:
+      label: To reproduce
+      placeholder: Steps to reproduce the behavior.
+    validations:
+      required: false
+  - type: textarea
+    id: expected
+    attributes:
+      label: Expected behavior
+      placeholder: A clear and concise description of what you expected to happen.
+    validations:
+      required: false

.github/ISSUE_TEMPLATE/config.yml

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+blank_issues_enabled: true