Contribution Guide added (#15).

CONTRIBUTING.md

+# Contributing
+
+
+## Issues
+
+**Issues** are used to report bugs, problems, feature requests, ask questions or other kind of suggestions. An issue ***should include***:
+
+- Good and meaningful title
+- Detailed description
+
+### Problems and Bugs
+
+Problem and bug reports ***need also***:
+
+- Expected and actual behaviour
+- Used version, compiler and platform
+- Minimal example or steps to reproduce
+
+
+## Pull Requests
+
+**Pull requests** are used to submit contributions to the project. A pull request ***should include***:
+
+- Good and meaningful title
+- Detailed description
+- Descriptive commit messages
+
+If the PR is related to an *Issue*, please reference it in the description or title.
+
+### Code
+
+The contributed code should match these criteria:
+
+- Pass all Unit Tests and CI Builds
+- Proper Test Cases
+- Merge cleanly, without conflicts
+- Follow the projects code style
+- Does not introduce external dependencies
+- 4 Spaces – no Tabs
+- UTF-8 encoding
+
+
+
+## Further readings
+
+- [Github Guide: How to Contribute to Open Source](https://opensource.guide/how-to-contribute/)
+