Create CODE_OF_CONDUCT.md

Adding code of conduct (same as the other Ember projects)

Author: MelSumner

CODE_OF_CONDUCT.md

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+The Ember team and community are committed to everyone having a safe and inclusive experience.
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+Our Community Guidelines / Code of Conduct can be found here:
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+https://emberjs.com/guidelines/
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+For a history of updates, see the page history here:
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+https://github.com/emberjs/website/commits/master/source/guidelines.html.erb