add link to CoC

Author: fmichonneau

bin/boilerplate/_config.yml

@@ -34,6 +34,7 @@ repository: <USERNAME>/<PROJECT>
 email: "team@carpentries.org"
 
 # Sites.
+coc: "https://docs.carpentries.org/topic_folders/policies/code-of-conduct.html"
 amy_site: "https://amy.carpentries.org/"
 carpentries_github: "https://github.com/carpentries"
 carpentries_pages: "https://carpentries.github.io"