feat(#118): Add CONTRIBUTING.md with development setup and guidelines (#129)

* plan(#118): initial brief from issue

* plan(#118): review brief

* plan(#118): apply brief review feedback

* plan(#118): review brief

* plan(#118): apply brief review feedback

* plan(#118): review brief

* plan(#118): create task breakdown

* feat(#118): add CONTRIBUTING.md and update README.md

Create CONTRIBUTING.md at the repository root covering prerequisites,
building, testing, code style, git workflow, pull request guidelines,
line endings, and cross-platform notes. Update README.md to link to
CONTRIBUTING.md from the contribution and development sections.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* feat(#118): implement tasks

* feat(#118): complete implementation

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: leecampbell-codeagent

CONTRIBUTING.md

@@ -0,0 +1,54 @@
+# Contributing
+
+Thank you for your interest in contributing to HdrHistogram.NET.
+We welcome pull requests and encourage contributors to engage with the project.
+
+## Prerequisites
+
+- .NET 8 SDK minimum (newer SDKs are also supported)
+- Supported platforms: Windows, macOS, Linux
+
+## Building
+
+```sh
+dotnet build HdrHistogram.sln
+```
+
+## Testing
+
+```sh
+dotnet test ./HdrHistogram.UnitTests/HdrHistogram.UnitTests.csproj -v q -c Release
+```
+
+## Code Style
+
+- Code style is governed by `.editorconfig`
+- Run `dotnet format` before submitting a PR
+- Use the .NET 8 SDK to match the CI environment
+
+## Git Workflow
+
+- Branch naming prefixes: `feat/`, `fix/`, `chore/`
+- One issue per PR
+- PRs target `main`
+- No direct commits to `main`
+
+## Pull Request Guidelines
+
+- Please first raise an issue before contributing so the team is not caught off guard by the pull request.
+- Ensure the PR has a comment describing what it achieves and which issues it closes.
+- If fixing an issue or bug, include a unit test proving the fix and reference the issue in the PR comments.
+
+## Line Endings
+
+- LF is the project convention.
+- `.gitattributes` normalises line endings automatically on checkout.
+- Windows batch files (`.cmd`, `.bat`) use CRLF by exception.
+- Keep `core.autocrlf=false` or rely on `.gitattributes` to handle line endings correctly.
+
+## Cross-Platform Notes
+
+- Shell scripts require LF line endings.
+- `.gitattributes` normalises line endings on checkout, so no manual intervention is needed.
+- All platforms (Windows, macOS, Linux) with the .NET 8 SDK can build and test natively with no container required.
+- `.devcontainer/` exists in the repository but contains agent-automation infrastructure only (`fleet.sh`, `agent-loop.sh`, etc.) and is not intended for human contributors.

README.md

@@ -256,13 +256,12 @@ histogram.OutputPercentileDistribution(
 
 ### How would I contribute to this project?
 
-We welcome pull requests!
-If you do choose to contribute, please first raise an issue so we are not caught off guard by the pull request.
-Next can you please ensure that your PR (Pull Request) has a comment in it describing what it achieves and the issues that it closes.
-Ideally if it is fixing an issue or a bug, there would be a Unit Test proving the fix and a reference to the Issues in the PR comments.
+See [CONTRIBUTING.md](CONTRIBUTING.md) for full contribution guidelines.
 
 ## Development
 
+For prerequisites and development setup, see [CONTRIBUTING.md](CONTRIBUTING.md).
+
 ### Running the Tests
 
 The unit tests can be run using `dotnet test`.