add contributing guidelines

Author: tiagoschenkel

CONTRIBUTING.md

@@ -0,0 +1,41 @@
+# Contributing to SignalsJS
+
+## Setup
+
+1 - Clone your fork of the repository:
+```
+$ git clone https://github.com/YOUR_USERNAME/SignalsJS.git
+```
+
+2 - Install npm dependencies using yarn:
+```
+$ yarn install
+```
+
+3 - Run start process
+```
+$ yarn start
+```
+
+4 - Run test process
+```
+$ yarn test
+```
+
+## Guidelines
+
+- Please try to [combine multiple commits before
+pushing](http://stackoverflow.com/questions/6934752/combining-multiple-commits-before-pushing-in-git)
+
+- Please use `TDD` when fixing bugs. This means that you should write a unit
+test that fails because it reproduces the issue, then fix the issue and finally run
+the test to ensure that the issue has been resolved. This helps us to prevent
+fixed bugs from happening again in the future.
+- Always format your code using `yarn run autoformat`.
+- Please keep the test coverage at 100%. Write additional unit test if
+necessary
+-  Please create an issue before sending a PR if your commit is going to change the
+public interface of SignalsJS or it includes significant architecture
+changes.
+- Feel free to ask for help from other members of the RobotlegsJS team via the
+chat or github issues.