Create a contribution guide

[fpindej]

Problem

Since this repository will be treated as a proper open-source project, it should have an easy-to-follow contribution guide to enable other people contribute and improve the library and codebase.

Solution suggestion

Create a contributing guide, use possible tools and get inspired by successful open-source projects

closes #101

[fpindej]

We might possibly use a generator from https://contributing.md/ and adjust it to our needs