Added CONTRIBUTING.md

Author: KevinRoebert

CONTRIBUTING.md

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+# Contribution Guidelines
+
+Thank you for your interest in contributing to ClearURLs! To keep our codebase secure, maintainable, and reviewable, please follow these guidelines when submitting Merge/Pull Requests.
+
+## Table of Contents
+
+1. [Getting Started](#getting-started)
+2. [Branching and Pull Requests](#branching-and-pull-requests)
+3. [Modifying Rules](#modifying-rules)
+4. [Adding New Rules](#adding-new-rules)
+5. [Testing Your Changes](#testing-your-changes)
+6. [Merge Request Size and Organization](#merge-request-size-and-organization)
+7. [Commit Messages](#commit-messages)
+8. [Security Considerations](#security-considerations)
+9. [Review Process](#review-process)
+
+---
+
+## Getting Started
+
+1. Fork the repository and create a new branch for your work.
+2. Sync with the upstream `master` branch regularly to avoid merge conflicts:
+   ```bash
+   git fetch upstream
+   git checkout master
+   git merge upstream/master
+   ```
+3. Create a topic branch with a descriptive name:
+   ```bash
+   git checkout -b add-new-tracking-rule
+   ```
+
+## Branching and Pull Requests
+
+- Use feature branches for each logical set of changes.
+- Don’t work directly on `master`.
+- Open a Merge Request (MR) / Pull Request (PR) against `master` when your feature branch is ready.
+
+## Modifying Rules
+
+> **Important:** Do **not** move, delete, or heavily modify existing rules in a single MR.
+
+- Existing rules in `rules.json` and `rules.min.json` must remain untouched. This prevents accidental removals and helps reviewers focus on new content.
+- If you need to refactor or clean up existing rules, create a dedicated MR for that purpose.
+
+## Adding New Rules
+
+1. **Append only:** Add new rules at the *end* of the file. Do not interleave with existing rules.
+2. **Rule format:** Follow the JSON schema and naming conventions exactly. See also https://docs.clearurls.xyz/latest/specs/rules/
+3. **Documentation:** For each new rule, include:
+   - A short description of its purpose.
+   - An example URL containing the tracking parameter(s) you intend to remove.
+   - (Optional) A brief note on any edge cases or limitations.
+
+## Merge Request Size and Organization
+
+- **Keep MRs small and focused.** Aim for fewer than 200 lines of net additions per MR.
+- **One topic per MR:** Group related rules together (e.g., all rules for a given domain).
+- If you have a large number of rules to add, split them into multiple MRs.
+
+## Commit Messages
+
+- Write clear, imperative commit messages.
+- Reference issue numbers when applicable: `Add rule for example.com (#123)`.
+
+## Security Considerations
+
+- ClearURLs is distributed as a browser extension and integrated into multiple applications, so any faulty or malicious rule could impact hundreds of thousands of users worldwide.
+- **Avoid large, unreviewable diffs:** split your changes into focused MRs so reviewers can thoroughly inspect each rule and prevent potential security issues.
+
+## Review Process
+
+- After opening an MR / PR, it will be assigned to a maintainer for review.
+- Respond promptly to review comments and clarify any questions.
+- Once approved and all CI checks pass, your MR will be merged.
+
+---
+
+We appreciate your contributions and efforts to keep ClearURLs secure and efficient! If you have any questions, feel free to open an issue or ask in the discussion channels.
+