meta: update CONTRIBUTING and pull request tempalte

.github/PULL_REQUEST_TEMPLATE/pull_request_template.md

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+<!--
+^ Please include a clear and concise description of the aim of your Pull Request above this line ^
+
+For plugin dependency/module additions, please make sure to link the source link of the added plugin
+or dependency in this section.
+
+If your pull request aims to fix an open issue or a please bug, please also link the relevant issue
+below this line. You may attach an issue to your pull request with `Fixes #<issue number>` outside
+this comment, and it will be closed when your pull request is merged.
+-->
+
+## Sanity Checking
+
+<!--
+Please check all that apply. As before, this section is not a hard requirement but checklists with more checked
+items are likely to be merged faster. You may save some time in maintainer review by performing self-reviews here
+before submitting your pull request.
+
+If your pull request includes any change or unexpected behaviour not covered below, please do make sure to include
+it above in your description.
+-->
+
+[editorconfig]: https://editorconfig.org
+[changelog]: https://github.com/NotAShelf/nvf/tree/main/docs/release-notes
+
+- [ ] I have updated the [changelog] as per my changes
+- [ ] I have tested, and self-reviewed my code
+- Style and consistency
+  - [ ] I ran **Alejandra** to format my code (`nix fmt`)
+  - [ ] My code conforms to the [editorconfig] configuration of the project
+  - [ ] My changes are consistent with the rest of the codebase
+- If new changes are particularly complex:
+  - [ ] My code includes comments in particularly complex areas
+  - [ ] I have added a section in the manual
+  - [ ] _(For breaking changes)_ I have included a migration guide
+- Package(s) built:
+  - [ ] `.#nix` (default package)
+  - [ ] `.#maximal`
+  - [ ] `.#docs-html` (manual, must build)
+- Tested on platform(s)
+  - [ ] `x86_64-linux`
+  - [ ] `aarch64-linux`
+  - [ ] `x86_64-darwin`
+  - [ ] `aarch64-darwin`
+
+<!--
+If your changes touch upon a portion of the codebase that you do not understand well, please make sure to consult
+the maintainers on your changes. In most cases, making an issue before creating your PR will help you avoid duplicate
+efforts in the long run.
+-->
+
+---
+
+Add a :+1: [reaction] to [pull requests you find important].
+
+[reaction]: https://github.blog/2016-03-10-add-reactions-to-pull-requests-issues-and-comments/
+[pull requests you find important]: https://github.com/NixOS/nixpkgs/pulls?q=is%3Aopen+sort%3Areactions-%2B1-desc