from #8518

As Piwik community is growing, it would be valuable to introduce a Code of Conduct which sets the tone of how we welcome all people to contribute, and pledge in return to value them as human beings and to foster an atmosphere of kindness, cooperation, and understanding.

Steps:

• Confirm that we want to use Contributor Code of Conduct 1.3.0
• Create a page piwik.org/conduct/ similar to http://rubyonrails.org/conduct/ / https://jquery.org/conduct/
• Add Code of conduct as Markdown file in root of piwik/piwik repository
• issue pull request here to be listed on Contributor Convenant
• Communicate as Blog post that the Code of Conduct is introduced in Piwik community