Add CONTRIBUTION guideline

[gribok]

Add CONTRIBUTION guideline for improved collaboration in the open source project. It enables a self-onboarding concept for developers.

Suggestion to cover some topics for version 0.1:

1. Coding Style (PEP8) in idiomic python way
2. Testcases for every change
3. Use issue tracker to find open enhancement with a badge
4. Use PR to publish changes

[ExpDev07]

Would be awesome if you could submit a PR for this 😍 . I can work on it too, no problem.

[Kilo59]

Can we adopt a formatter and/or import sorter?
My preference is black.

[ExpDev07]

Absolutely @Kilo59

[gribok]

I will submit a PR. Please assign issue to myself.
@Kilo59 For formatter discussion, please raise another issue.

[Kilo59]

I will submit a PR. Please assign issue to myself.
@Kilo59 For formatter discussion, please raise another issue.

The style guide, linter and formatter decisions need to be made holistically. Otherwise they are liable to conflict.