Update developer documentation

[magicant]

This pull request introduces new and expanded documentation to help contributors and users understand how to work with the Yash shell project. The most important changes are the addition of a comprehensive contributing guide, improved documentation for writing completion scripts, and expanded instructions for writing and running automated tests.

General Documentation Improvements

• Added a new CONTRIBUTING.md file with detailed instructions for contributing to code, documentation, completion scripts, and translations, including guidelines for asking questions, reporting bugs, and proposing new features.
• Removed the now-redundant TRANSLATING.md file, consolidating translation instructions into the new contributing guide.

Completion Scripts Documentation

• Added a thorough guide to share/completion/README.md explaining how to write completion scripts for Yash, including file structure, core concepts, utility functions, and examples.

Automated Testing Documentation

• Expanded tests/README.md to include an introduction and detailed instructions on writing test cases using the provided test harness, with examples and explanation of available options and aliases. [1] [2]

[Copilot]

Pull Request Overview

This pull request improves developer documentation by consolidating and expanding guidance for contributors and users. The changes focus on creating a comprehensive contributing guide, adding thorough documentation for completion scripts, and enhancing test writing instructions.

• Added a new comprehensive CONTRIBUTING.md file with guidelines for all types of contributions
• Removed redundant TRANSLATING.md file, consolidating translation instructions into the contributing guide
• Enhanced documentation for writing completion scripts and test cases

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
CONTRIBUTING.md	New comprehensive guide covering code contributions, documentation, completion scripts, and translations
tests/README.md	Added detailed section on writing test cases with examples and harness documentation
share/completion/README.md	New thorough guide explaining how to write completion scripts for Yash
TRANSLATING.md	File removed as content was consolidated into CONTRIBUTING.md

Comments suppressed due to low confidence (1)

tests/README.md:7

• Grammar error: 'does not' should be 'do not' to agree with the plural subject 'test cases'.

shell is supposed to pass the POSIX tests, so those test cases does not

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[Copilot]

[nitpick] The documentation mentions passing -P \"$PREFIX\" but doesn't show this in any of the examples above. Consider adding an example demonstrating this usage for clarity.