It's a good idea to add the files to our repository. I suggest we use exactly the same those from Gutenberg which would apply just like that to this repository as well:

• https://github.com/WordPress/gutenberg/blob/trunk/CODE_OF_CONDUCT.md
• https://github.com/WordPress/gutenberg/blob/trunk/SECURITY.md

In the PR that adds these two files, it may also be good to update the CONTRIBUTING.md file (from #47) to link to those - we could use the exact same content from the Gutenberg repository (see https://github.com/WordPress/gutenberg/blob/trunk/CONTRIBUTING.md#guidelines and https://github.com/WordPress/gutenberg/blob/trunk/CONTRIBUTING.md#reporting-security-issues) as well.