docs: enhance contributing guide with industry standards

Co-Authored-By: Claude <[email protected]>

Author: marc0der

CONTRIBUTING.md

@@ -1,15 +1,114 @@
-## Contributing
+# Contributing to SDKMAN! CLI
 
-We greatly value the feedback and contributions of our users.
+Thank you for your interest in contributing to SDKMAN! CLI. We greatly value the feedback and contributions of our users.
 
-We distinguish between Bugs/Issues, New Features and Support Requests. We also try to minimise the noise in our GitHub Issues stream and prefer having a conversation on [SDKMAN Discord](https://discord.gg/y9mVJYVyu4) before creating new issues if you are not entirely sure how to categorize your request. Sign up and join our Help channel.
+## Important Notice
 
-The [GitHub Issue Tracker](https://github.com/sdkman/sdkman-cli/issues/new) provides templates for required information.
+**This project is in maintenance mode.** We are only accepting bug fixes at this time, as SDKMAN! CLI is being rewritten in Rust. New features and enhancements will not be accepted.
 
-**Unfortunately, we might close any GitHub Issues that have not followed the requested template.**
+## Code of Conduct
 
-### Pull Requests
+This project adheres to the [Contributor Covenant Code of Conduct](CODE_OF_CONDUCT.md). By participating, you are expected to uphold this code. Please report unacceptable behavior to [email protected].
 
-Pull Requests are _always_ very welcome but require a valid GitHub Issue as described above. The PR template is to be filled in before submission, ensuring that it is _linked back_ to the GitHub Issue number by replacing `#XXX` with the appropriate issue reference.
+## How to Contribute
 
-Each PR should also be accompanied by a passing test(s) proving its validity (where feasible). The feasibility of the test will emerge in the initial discussions of the issue.
+### Before You Start
+
+We distinguish between:
+- **Bug Reports**: Issues with existing functionality
+- **Support Requests**: Questions about usage
+
+We prefer to have a conversation on [SDKMAN Discord](https://discord.gg/y9mVJYVyu4) before creating new issues if you're unsure how to categorize your request. Join our Help channel to discuss.
+
+### Reporting Bugs
+
+1. **Search existing issues** to avoid duplicates
+2. **Use the issue template** when creating a new issue via our [GitHub Issue Tracker](https://github.com/sdkman/sdkman-cli/issues/new)
+3. **Provide detailed information** including:
+   - Steps to reproduce the issue
+   - Expected behavior
+   - Actual behavior
+   - Your environment (OS, shell, Java version)
+   - Relevant logs or error messages
+
+**Note:** Issues that don't follow the template may be closed.
+
+### Submitting Pull Requests
+
+Pull requests are always welcome but must follow these guidelines:
+
+#### Prerequisites
+
+1. **Link to an issue**: Every PR must reference a valid GitHub issue
+2. **Discuss first**: Talk about your proposed fix on Discord or in the issue before starting work
+3. **Keep it small**: Small, focused PRs are strongly preferred over large changes
+4. **Include tests**: Each PR should include passing tests that prove its validity (where feasible)
+
+#### Development Setup
+
+1. **Install required tools**:
+   ```bash
+   sdk env install  # Install JDK 11 from .sdkmanrc
+   sdk env          # Switch to correct SDK versions
+   ```
+
+2. **Verify your setup**:
+   ```bash
+   ./gradlew test
+   ```
+
+#### Development Workflow
+
+1. **Fork the repository** and create a new branch from `master`
+2. **Make your changes** following our code standards
+3. **Write or update tests** to cover your changes
+4. **Run the test suite** to ensure everything passes:
+   ```bash
+   ./gradlew test
+   ```
+5. **Commit your changes** using clear, descriptive commit messages
+6. **Push to your fork** and submit a pull request
+
+#### Pull Request Guidelines
+
+- Fill in the PR template completely
+- Link back to the GitHub issue by replacing `#XXX` with the issue number
+- Ensure all tests pass
+- Keep commits focused and atomic
+- Write clear commit messages in imperative mood (e.g., "fix user login bug")
+- Be responsive to feedback during code review
+
+#### Testing Requirements
+
+- All bug fixes must include a test that would have caught the bug
+- Tests should follow the existing Cucumber BDD pattern
+- Tests should cover both happy path and edge cases
+- Run `./gradlew test` to verify all tests pass
+
+### Code Standards
+
+- Follow the existing code style in bash scripts
+- Use meaningful variable and function names
+- Add comments for complex logic
+- Avoid introducing new dependencies without discussion
+- Ensure backward compatibility
+
+### Getting Help
+
+- Join our [Discord server](https://discord.gg/y9mVJYVyu4) for questions
+- Check existing issues and discussions
+- Read the documentation in the repository
+
+## Project Structure
+
+- `src/main/bash/` - Core bash scripts implementing SDKMAN commands
+- `src/test/groovy/` - Groovy test code using Spock framework
+- `src/test/resources/features/` - Cucumber feature files (BDD tests)
+
+## Recognition
+
+Contributors will be recognized in our release notes and commit history. We appreciate your efforts to make SDKMAN! better!
+
+## Questions?
+
+If you have questions about contributing, feel free to ask on [Discord](https://discord.gg/y9mVJYVyu4) or open a discussion on GitHub.