contribution and code of conduct (#1)

CONTRIBUTING.md

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+# Contributing to MLX
+
+We want to make contributing to this project as easy and transparent as
+possible.
+
+## Pull Requests
+
+1. Fork and submit pull requests to the repo. 
+2. If you've added code that should be tested, add tests.
+3. If a change is likely to impact efficiency, run some of the benchmarks before
+   and after the change. Examples of benchmarks can be found in `benchmarks/python/`.
+4. If you've changed APIs, update the documentation.
+5. Every PR should have passing tests and at least one review. 
+6. For code formating install `pre-commit` using something like `pip install pre-commit` and run `pre-commit install`.
+   This should install hooks for running `black` and `clang-format` to ensure
+   consistent style for C++ and python code.
+ 
+   You can also run the formatters manually as follows:
+ 
+     ```
+     clang-format -i file.cpp
+     ```
+ 
+     ```
+     black file.py
+     ```
+ 
+   or run `pre-commit run --all-files` to check all files in the repo.
+
+## Issues
+
+We use GitHub issues to track public bugs. Please ensure your description is
+clear and has sufficient instructions to be able to reproduce the issue.
+
+## License
+
+By contributing to MLX, you agree that your contributions will be licensed
+under the LICENSE file in the root directory of this source tree.