Add contributing guideline and mypy config (#122)

CONTRIBUTING.md

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+# Contributing to CacheFlow
+
+Thank you for your interest in contributing to CacheFlow!
+Our community is open to everyone and welcomes all kinds of contributions, no matter how small or large.
+There are several ways you can contribute to the project:
+
+- Identify and report any issues or bugs.
+- Request or add a new model.
+- Suggest or implement new features.
+
+However, remember that contributions aren't just about code.
+We believe in the power of community support; thus, answering queries, assisting others, and enhancing the documentation are highly regarded and beneficial contributions.
+
+Finally, one of the most impactful ways to support us is by raising awareness about CacheFlow.
+Talk about it in your blog posts, highlighting how it's driving your incredible projects.
+Express your support on Twitter if CacheFlow aids you, or simply offer your appreciation by starring our repository.
+
+
+## Setup for development
+
+### Build from source
+
+```bash
+pip install -r requirements.txt
+pip install -e .  # This may take several minutes.
+```
+
+### Testing
+
+```bash
+pip install -r requirements-dev.txt
+
+# Static type checking
+mypy
+# Unit tests
+pytest tests/
+```
+**Note:** Currently, the repository does not pass the mypy tests.
+
+
+## Contributing Guidelines
+
+### Issue Reporting
+
+If you encounter a bug or have a feature request, please check our issues page first to see if someone else has already reported it.
+If not, please file a new issue, providing as much relevant information as possible.
+
+### Coding Style Guide
+
+In general, we adhere to [Google Python style guide](https://google.github.io/styleguide/pyguide.html) and [Google C++ style guide](https://google.github.io/styleguide/cppguide.html).
+
+### Pull Requests
+
+When submitting a pull request:
+
+1. Make sure your code has been rebased on top of the latest commit on the main branch.
+2. Include a detailed description of the changes in the pull request.
+Explain why you made the changes you did.
+If your pull request fixes an open issue, please include a reference to it in the description.
+
+### Code Reviews
+
+All submissions, including submissions by project members, require a code review.
+To make the review process as smooth as possible, please:
+
+1. Keep your changes as concise as possible.
+If your pull request involves multiple unrelated changes, consider splitting it into separate pull requests.
+2. Respond to all comments within a reasonable time frame.
+If a comment isn't clear or you disagree with a suggestion, feel free to ask for clarification or discuss the suggestion.
+
+### Thank You
+
+Finally, thank you for taking the time to read these guidelines and for your interest in contributing to CacheFlow.
+Your contributions make CacheFlow a great tool for everyone!