doc: Add empty development section

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doc
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doc/development.md
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# Development of Nixpkgs {#part-development}
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This section shows you how Nixpkgs is being developed and how you can interact with the contributors and the latest updates.
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If you are interested in contributing yourself, see [CONTRIBUTING.md](https://github.com/NixOS/nixpkgs/blob/master/CONTRIBUTING.md).
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<!-- In the future this section should also include: How to open issues (request backports, request updates, report bugs, ...), how to test pull requests, how to know if pull requests are available in channels, etc. -->
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doc/manual.md.in
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lib.md
stdenv.md
builders.md
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development.md
contributing.md
```