Add CoC information in documentation site
project needs.
</p>
<p>
- {{ copyright }} The website content uses the <a href="https://github.com/bokeh/demo.bokeh.org/blob/master/LICENSE.txt">BSD License</a>.
+ {{ copyright }} The website content uses the <a href="https://github.com/bokeh/demo.bokeh.org/blob/master/LICENSE.txt">BSD License</a> and is covered by the <a href="https://github.com/bokeh/bokeh/blob/master/CODE_OF_CONDUCT.md">Bokeh Code of Conduct</a>.
</p>
</div>
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