Add CODE-OF-CONDUCT.md, point to website

It seems most CNCF projects provide a CODE-OF-CONDUCT.md file at the
root of their repositories, even if they have their Code of Conduct on
their website. To better fit into the CNCF ecosystem and be a more
welcoming project, follow that pattern.

Relates-to: submariner-io/submariner#804
Signed-off-by: Daniel Farrell <dfarrell@redhat.com>

CODE-OF-CONDUCT.md

@@ -0,0 +1,3 @@
+# Code of Conduct
+
+Please see the [Code of Conduct docs on Submariner's website](https://submariner.io/contributing/code-of-conduct/).

CONTRIBUTING.md

@@ -0,0 +1,3 @@
+# Contributing
+
+Please see the [Contributing docs on Submariner's website](https://submariner.io/contributing/).