[DOCS] adding contributing guideline

CONTRIBUTING.md

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+# How to contribute to Ygen
+#### Did you find a bug?
+ - **Ensure the bug was not already reported** by searching trough the Issues
+ - If there isn't already an open Issue open a new one. Be sure to follow write it
+   And follow the Issue Bug template
+
+#### Did you fixed a bug?
+ - Open a Pull Request with the fix
+ - Make sure you reference the Issue with the description of the bug
+ - Provide a clear description on how you fixed the bug and what it caused
+
+#### Did you added a cosmetic change?
+  - **Cosmatic changes will mostly likly be not accepted** when submitted via Pull Request
+  - But if you find an function or a variable which doesn't follow our naming sceme (funcAbcDefg instead of func_abc_defg) please create an Issue
+
+#### Do you want to add a new feature?
+  - **Introduce it via a Issue**, when it gets approved you can start working on it
+    (You can start working on it right now without adding an Issue but then you're having the change that your feature will maybe get rejected)
+  - **Then create a Pull Request**
+
+#### Do you have questions about the source code?
+  - Feel free to ask in our Discord Server or **create a Issue**
+
+Thanks!
+The **Ygen** Team