update CONTRIBUTING.md file
minor #506 update CONTRIBUTING.md file (keradus)

This PR was merged into the 1.0.x-dev branch.

Discussion
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update CONTRIBUTING.md file

Changes due to using gh tool.
- no need to prefix PR with `bug` etc - it will make ugly automatic merge messages.
- no need to squash commits

Commits
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3c3e507 update CONTRIBUTING.md file