Adding contributing guide explaining how to setup the precommit hook

CONTRIBUTING.md

@@ -0,0 +1,58 @@
+# Contributing to WorkAdventure
+
+Are you looking to help on WorkAdventure? Awesome, feel welcome and read the following sections in order to know how to 
+ask questions and how to work on something.
+
+## Contributions we are seeking
+
+We love to receive contributions from our community — you!
+
+There are many ways to contribute, from writing tutorials or blog posts, improving the documentation, 
+submitting bug reports and feature requests or writing code which can be incorporated into WorkAdventure itself.
+
+## Using the issue tracker
+
+First things first: **Do NOT report security vulnerabilities in public issues!**.
+Please read the [security guide](SECURITY.md) to learn who to do a security disclosure to the WorkAdventure core team.
+
+You can use [GitHub issue tracker](https://github.com/thecodingmachine/workadventure/issues) to:
+
+- File bug reports
+- Ask for feature requests
+
+If you have more general questions, a good place to ask is [our Discord server](https://discord.gg/YGtngdh9gt).
+
+Finally, you can come and talk to the WorkAdventure core team... on WorkAdventure, of course! [Our offices are here](https://play.staging.workadventu.re/@/tcm/workadventure/wa-village).
+
+## Pull requests
+
+Good pull requests - patches, improvements, new features - are a fantastic help. They should remain focused in scope 
+and avoid containing unrelated commits.
+
+Please ask first before embarking on any significant pull request (e.g. implementing features, refactoring code), 
+otherwise you risk spending a lot of time working on something that the project's developers might not want to merge 
+into the project.
+
+You can ask us on [Discord](https://discord.gg/YGtngdh9gt) or in the [GitHub issues](https://github.com/thecodingmachine/workadventure/issues).
+
+### Linting your code
+
+Before committing, be sure to install the "Prettier" precommit hook that will reformat your code to our coding style.
+
+In order to enable the "Prettier" precommit hook, at the root of the project, run:
+
+```console
+$ yarn run install
+$ yarn run prepare
+```
+
+### Providing tests
+
+WorkAdventure is based on a video game engine (Phaser), and video games are not the easiest programs to unit test.
+
+Nevertheless, if your code can be unit tested, please provide a unit test (we use Jasmine).
+
+If you are providing a new feature, you should setup a test map in the `maps/tests` directory. The test map should contain
+some description text describing how to test the feature. Finally, you should modify the `maps/tests/index.html` file
+to add a reference to your newly created test map.
+