docs(contributing): add contribution guidelines for the flutter_policy_engine project

Author: dgarciasquare1

CONTRIBUTING.md

@@ -0,0 +1,91 @@
+# Contributing to flutter_policy_engine
+
+Thank you for your interest in contributing! We welcome contributions from everyone. If you are not a direct collaborator, please follow the **fork-and-pull-request** workflow described below.
+
+## Branch Strategy
+
+- **develop**: All external pull requests must target the `develop` branch. This is where active development happens.
+- **main**: The `main` branch is reserved for stable releases. It is updated internally by the maintainers via a pull request from `develop` to `main`.
+- **Do not submit pull requests directly to `main`.**
+
+## 1. Prerequisites
+
+- Ensure you have a [GitHub account](https://github.com/).
+- Install [Git](https://git-scm.com/) and [Flutter](https://flutter.dev/docs/get-started/install) on your machine.
+- Familiarize yourself with our [README.md](./README.md) and project structure.
+
+## 2. Forking the Repository
+
+- Navigate to the [flutter_policy_engine GitHub page](https://github.com/your-org/flutter_policy_engine).
+- Click the **Fork** button (top right) to create your own copy of the repository.
+
+## 3. Cloning Your Fork
+
+- Clone your fork to your local machine:
+  ```sh
+  git clone https://github.com/your-username/flutter_policy_engine.git
+  cd flutter_policy_engine
+  ```
+
+## 4. Creating a Feature Branch
+
+- Always create a new branch for your work:
+  ```sh
+  git checkout -b feature/your-feature-name
+  ```
+- Use descriptive branch names (e.g., `feature/add-logging`, `fix/null-pointer-issue`).
+
+## 5. Making Changes
+
+- Make your changes in the appropriate files.
+- Follow the language and framework conventions (Dart/Flutter best practices).
+- Write clear, self-documenting code. Add docstrings for public APIs and explain the "why" in comments if needed.
+- Add or update tests for your changes.
+
+## 6. Keeping Your Fork Up to Date
+
+- Sync your fork with the upstream repository to avoid merge conflicts:
+  ```sh
+  git remote add upstream https://github.com/your-org/flutter_policy_engine.git
+  git fetch upstream
+  git merge upstream/develop
+  ```
+
+## 7. Commit Messages
+
+- Write concise, meaningful commit messages.
+- Use the present tense (e.g., "Add feature X", "Fix bug Y").
+- Group related changes into a single commit when possible.
+
+## 8. Submitting a Pull Request
+
+- Push your branch to your fork:
+  ```sh
+  git push origin feature/your-feature-name
+  ```
+- Go to your fork on GitHub and click **Compare & pull request**.
+- **Set the base branch to `develop` in the main repository.**
+- Fill out the PR template, describing your changes and referencing any related issues.
+- Submit the pull request to the `develop` branch.
+
+## 9. Code Review Process
+
+- Your PR will be reviewed by maintainers.
+- Be responsive to feedback and make requested changes.
+- Once approved, your PR will be merged into `develop`.
+- The `main` branch is updated internally by maintainers via a separate pull request from `develop` to `main`.
+
+## 10. Additional Guidelines
+
+- Ensure all tests pass before submitting your PR.
+- Follow our code style and linting rules (see `analysis_options.yaml`).
+- Do not include unrelated changes in your PR.
+- If your change is significant, consider updating the documentation.
+
+## 11. Contact
+
+If you have questions, open an issue or contact the maintainers via GitHub Discussions or Issues.
+
+---
+
+Thank you for helping make this project better!