docs: Adding CONTRIBUTING.md

adding guidelines for contributors.

Author: khushhalm

CONTRIBUTING.md

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+Read our [Code of Conduct](CODE_OF_CONDUCT.md) to keep our community approachable and respectable.
+
+This guide will give you an overview of the contribution workflow from opening an issue, creating a PR, reviewing, and merging the PR.
+
+# Local Setup
+- Follow https://github.com/browserstack/enigma-public-central#setup for setting up the project locally.
+
+# Issues
+
+## Create a new issue
+If you spot an issue with the tool or you want to improve the tool by adding some functionality, search if an issue already exists for the same. 
+
+If you're unable to find an open issue addressing the problem, open a new one. Be sure to include a title and clear description, as much relevant information as possible, and a code sample or an executable test case demonstrating the expected behavior that is not occurring.
+
+ ## Solve an issue
+Scan through our existing issues to find one that interests you. You can narrow down the search using labels as filters. As a general rule, we don’t assign issues to anyone. If you find a problem to work on, you are welcome to open a PR with a fix.
+
+## Did you write a patch that fixes a bug or adds functionality?
+- Commit the changes once you are happy with them. Always write a clear log message for your commits. 
+  - For commit message we follow [Conventional Commit Message Guideline](https://www.conventionalcommits.org). To enforce this we use [pre-commit](https://pre-commit.com), to setup the same go through [pre-commit setup section of the README](https://github.com/browserstack/enigma-public-central#for-contributing-code)
+  - Make sure there are no lint issues, check lint issues by running `make lint`. If there are some in the portion which you have touched, fix those lint issues.
+  - If you are making changes to config then please update [schema.json file](schema.json) also.
+  - We use [semgrep](https://semgrep.dev) for static code analysis and finding vulnerabilities. To check issues locally run `make run_semgrep`.
+- Please test the tool locally so that by doing the above change there is nothing breaking in the project elsewhere.
+  - To test project locally you can run `make test`
+- Don't forget to self-review to speed up the review process.
+- Open a new GitHub pull request with the fix/patch.
+- Ensure the PR description clearly describes the problem and solution. Include the relevant issue number if applicable.
+- Before submitting, please read the [Contributing to Django project](https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/) guide to know more about coding conventions and unit tests, etc.
+- Your PR is merged!
+- Congratulations 🎉 The Enigma team thanks you ✨.
+- Once your PR is merged, your contributions will be publicly visible on the Project Repo.
+
+## Coding conventions
+[Coding style | Django documentation](https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/coding-style/)
+