Check markdown format

[stefaniuk]

The intent of this PR is to:

• Add markdown format linter to be run on changed files as a GitHub workflow action
• Move the CONTRIBUTING.md file to the top level as this would be a default place for most repositories, rather than being a bit hidden in the .github directory (this has been done in fact to trigger the action and test if it works as expected)

[sonarcloud[bot]]

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