update CONTRIBUTING.md

CONTRIBUTING.md

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 # Contributing to moonbitlang/core
+
+## Step 0: Contributor License Agreement
+
+Before sending your first change to the moonbitlang/core project you must have completed one of the following two CLAs. Which CLA you should sign depends on who owns the copyright to your work.
+
+- Individual contributor license agreement.
+- Corporate contributor license agreement.
+
+
+## Step 1: Clone the repository
+
+To start working on the project, you need to have a local copy of the repository. You can obtain one by cloning the repository using the following Git command:
+
+```bash
+git clone https://github.com/moonbitlang/core
+```
+
+This command will create a copy of the repository on your local machine, allowing you to make changes.
+
+
+## Step 2: Make your change
+
+Now it's time to make your changes to the codebase. Whether it's fixing a bug, adding a new feature, or improving documentation, your contributions are welcome. Ensure that your changes are clear and understandable to others who will be reviewing your code.
+
+## Step 3: Test your change
+
+After making your changes, it's important to test them to ensure they work as expected and do not introduce new issues. You can run the following commands to test your changes:
+
+```bash
+moon check
+moon test
+moon bundle
+```
+
+## Step 4: Submit a pull request and request a review
+
+Simply follow the standard [GitHub flow](https://docs.github.com/en/get-started/using-github/github-flow) to submit your pull request. 
+
+After submitting your pull request, request a review from the project maintainers or other contributors.