## Description
just a little refactor of `CONTRIBUTING.md` of the standard library in
`nu-std`.
- see the new version
[here](https://github.com/amtoine/nushell/blob/stblib/refactor/CONTRIBUTING-guidelines/crates/nu-std/CONTRIBUTING.md).
> **Note**
> actually, that one might be best reviewed commit by commit 😋
> i tried to be as explicit as possible 😌
- i fixed the width to `80` columns
- cc/ @bobhy, if you want to jump in and find broken links / bad changes
# Description
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Replaces #8824, which was languishing in review limbo and becoming
increasingly difficult to keep current with upstream changes.
In addition to all the edits, this PR includes updated documentation for
running unit tests via `std run-tests`.
# User-Facing Changes
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helps us keep track of breaking changes. -->
A CONTRIBUTING.md documenting guidelines and getting started info for
potential stdlib contributors.
# Tests + Formatting
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# After Submitting
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