docs: Add Contributing guides

Author: mrmlnc

CONTRIBUTING.md

@@ -0,0 +1,57 @@
+# Contributing to my package
+
+Welcome, and thank you for your interest in contributing to **vscode-csscomb**!
+
+Please note that this project is released with a [Contributor Code of Conduct](CODE-OF-CONDUCT.md). By participating in this project you agree to abide by its terms.
+
+## Contribution Guidelines
+
+There are a couple of ways you can contribute to this repo:
+
+  * **Ideas, feature requests and bugs**: We are open to all ideas and we want to get rid of bugs! Use the [Issues section](https://github.com/mrmlnc/vscode-csscomb/issues) to either report a new issue, provide your ideas or contribute to existing threads.
+  * **Documentation**: Found a typo or strangely worded sentences? Submit a PR!
+  * **Code**: Contribute bug fixes, features or design changes.
+
+### Creating an Issue
+
+Before you create a new Issue:
+
+  * Check the [Issues](https://github.com/mrmlnc/vscode-csscomb/issues) on Github to ensure one doesn't already exist.
+  * Clearly describe the issue, including the steps to reproduce the issue.
+
+### Making Changes
+
+#### Getting Started
+
+  * Install [Node.js](https://nodejs.org/en/).
+  * Fork the project and clone the fork repo. ([how to create fork?](https://help.github.com/articles/fork-a-repo/#fork-an-example-repository)).
+  * Create a topic branch from the master branch.
+  * Run `yarn` or `npm install` to install the application dependencies.
+
+#### Setup
+
+1. Start watching:
+
+```
+$ npm run watch
+```
+
+2. Make changes:
+
+```
+$ code .
+```
+
+3. Run tests:
+
+```
+$ npm t
+```
+
+4. Test your version of the extension:
+
+Press <kbd>F5</kbd> in the editor and then test extension commands and functions.
+
+#### Commit
+
+Keep git commit messages clear and appropriate. You can use [Angular guide](https://github.com/angular/angular.js/blob/master/DEVELOPERS.md#-git-commit-guidelines).