Add a contributing guide

CONTRIBUTING.md

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+## How to contribute code
+
+Follow these steps to submit your code contribution.
+
+### Step 1. Open an issue
+
+Before making any changes, we recommend opening an issue (if one doesn't already
+exist) and discussing your proposed changes. This way, we can give you feedback
+and validate the proposed changes.
+
+If your code change involves the fixing of a bug, please include a 
+[Colab](https://colab.research.google.com/) notebook that shows
+how to reproduce the broken behavior.
+
+If the changes are minor (simple bug fix or documentation fix), then feel free
+to open a PR without discussion.
+
+### Step 2. Make code changes
+
+To make code changes, you need to fork the repository. You will need to setup a
+development environment and run the unit tests. This is covered in section
+"Setup environment".
+
+### Step 3. Create a pull request
+
+Once the change is ready, open a pull request from your branch in your fork to
+the master branch in [keras-team/keras-cv](https://github.com/keras-team/keras-cv).
+
+### Step 4. Sign the Contributor License Agreement
+
+After creating the pull request, you will need to sign the Google CLA agreement. 
+The agreement can be foiund at [https://cla.developers.google.com/clas](https://cla.developers.google.com/clas).
+
+
+### Step 5. Code review
+
+CI tests will automatically be run directly on your pull request.  Their
+status will be reported back via GitHub actions.
+
+There may be
+several rounds of comments and code changes before the pull request gets
+approved by the reviewer.
+
+![Approval from reviewer](https://i.imgur.com/zgRziTt.png)
+
+### Step 6. Merging
+
+Once the pull request is approved, a team member will take care of merging.
+
+## Setup environment
+
+Setting up your KerasCV development environment requires you to fork the KerasCV repository,
+clone the repository, install dependencies, and execute `python setup.py develop`.
+
+You can achieve this by running the following commands:
+
+```shell
+gh repo fork keras-team/keras-cv --clone --remote
+cd keras-cv
+pip install ".[tests]"
+python setup.py develop
+```
+
+The first line relies on having an installation of [the GitHub CLI](https://github.com/cli/cli).
+
+Following these commands you should be able to run the tests using `pytest keras_cv`.
+Please report any issues running tests following these steps.
+
+## Run tests
+
+KerasCV is tested using [PyTest](https://docs.pytest.org/en/6.2.x/).
+
+### Run a test file
+
+To run a test file, run `pytest path/to/file` from the root directory of keras\_cv.
+
+### Run a single test case
+
+To run a single test, you can use `-k=<your_regex>`
+to use regular expression to match the test you want to run. For example, you
+can use the following command to run all the tests in `cut_mix_test.py`,
+whose names contain `label`,
+
+```
+pytest keras_cv/layers/preprocessing/cut_mix_test.py -k="label"
+```
+
+### Run all tests
+
+You can run the unit tests for KerasCV by running:
+```
+pytest keras_cv/
+```
+
+## Formatting the Code
+We use `flake8`, `isort` and `black` for code formatting.  You can run
+the following commands manually every time you want to format your code:
+
+- Run `shell/format.sh` to format your code
+- Run `shell/lint.sh` to check the result.
+
+If after running these the CI flow is still failing, try updating `flake8`, `isort` and `black`.
+This can be done by running `pip install --upgrade black`, `pip install --upgrade flake8`, and 
+`pip install --upgrade isort`.
+
+## Community Guidelines
+
+This project follows [Google's Open Source Community Guidelines](https://opensource.google/conduct/).
+