chore: adds contributing guide

CONTRIBUTING.md

@@ -0,0 +1,38 @@
+## How to contribute to Whenever
+
+#### **Did you find a bug?**
+
+* **Ensure the bug was not already reported** by searching on GitHub under [Issues](https://github.com/your/whenever/issues).
+
+* If you're unable to find an open issue addressing the problem, [open a new one](https://github.com/your/whenever/issues/new). 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.
+
+#### **Did you write a patch that fixes a bug?**
+
+* Open a new GitHub pull request with the patch.
+
+* Ensure the PR description clearly describes the problem and solution. Include the relevant issue number if applicable.
+
+
+#### **Do you have questions about the source code?**
+
+* Ask any question about how to use Whenever in the [whenever issues](https://github.com/javan/whenever/issues).
+
+#### **Do you want to contribute to the Whenever documentation?**
+
+Whenever is a volunteer effort. We encourage you to pitch in! 
+
+Thanks! :heart: :heart: :heart:
+
+Whenever Team
+
+---
+## Setup
+
+```bash
+$ bundle install
+```
+## Run tests
+
+```bash
+$ make test
+```