Add link to code of conduct to community index page
Add link to code of conduct to community index page

The code of conduct is important and should be mentioned here.

Signed-off-by: Edwin Kempin <d43fb6c98c97e553b671ed9a9318100f1de386e7@google.com>
Change-Id: I8c22d19c6540b1a15ba64b1988a0099706c47e94

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