docs: added CONTRIBUTING.md (#188)

* Create CONTRIBUTING.md

* docs: added contributing.md

Co-authored-by: Vasu Gamdha <40864108+vasugamdha@users.noreply.github.com>

CONTRIBUTING.md

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+# Contributing to [github-readme-stats](https://github.com/anuraghazra/github-readme-stats)
+
+We love your input! We want to make contributing to this project as easy and transparent as possible, whether it's:
+
+- Reporting a issue
+- Discussing the current state of the code
+- Submitting a fix
+- Proposing new features
+- Becoming a maintainer
+
+## All Changes Happen Through Pull Requests
+
+Pull requests are the best way to propose changes. We actively welcome your pull requests:
+
+1. Fork the repo and create your branch from `master`.
+1. If you've added code that should be tested, add some tests' example.
+1. If you've changed APIs, update the documentation.
+1. Issue that pull request!
+
+## Local Development
+
+To run & test github-readme-stats you need to follow few simple steps :-
+_(make sure you already have a [vercel](https://vercel.com/) account)_
+
+1. Install [Vercel CLI](https://vercel.com/download)
+1. Fork the repository and clone the code to your local machine
+1. Run the command "vercel" in the root and follow the steps there
+1. Create a `.env` file in the root of the directory
+1. In the .env file add a new variable named "PAT" with your [github Personal access token](https://docs.github.com/en/github/authenticating-to-github/creating-a-personal-access-token)
+1. Run the command "vercel dev" to start a development server at https://localhost:3000
+
+## Themes Contribution
+
+Github readme stats supports custom theming and you can also contribute new themes!
+
+All you need to do is edit [themes/index.js](./themes/index.js) file and add your theme at the end of the file.
+
+While creating the Pull request to add a new theme **don't forget to add a screenshot of how your theme looks**, you can also test how it looks using custom url parameters like `title_color`, `icon_color`, `bg_color`, `text_color`
+
+> NOTE: If you are contributing your theme just because you are using it personally, then you can [customize the looks](./readme.md#customization) of your card with URL params instead.
+
+## Any contributions you make will be under the MIT Software License
+
+In short, when you submit changes, your submissions are understood to be under the same [MIT License](http://choosealicense.com/licenses/mit/) that covers the project. Feel free to contact the maintainers if that's a concern.
+
+## Report issues/bugs using Github's [issues](https://github.com/anuraghazra/github-readme-stats/issues)
+
+We use GitHub issues to track public bugs. Report a bug by [opening a new issue](https://github.com/anuraghazra/github-readme-stats/issues/new/choose); it's that easy!
+
+### Bug Reports
+
+**Great Bug Reports** tend to have:
+
+- A quick summary and/or background
+- Steps to reproduce
+  - Be specific!
+  - Share the snapshot, if possible.
+  - Github Readme Stats' live link
+- What actually happens
+- What you expected would happen
+- Notes (possibly including why you think this might be happening, or stuff you tried that didn't work)
+
+People _love_ thorough bug reports. I'm not even kidding.
+
+### Feature Request
+
+**Great Feature Requests** tend to have:
+
+- A quick idea summary
+- What & why you wanted to add the specific feature
+- Additional Context like images, links to resources to implement the feature etc etc.
+
+## License
+
+By contributing, you agree that your contributions will be licensed under its [MIT License](./LICENSE).