Add banner to docs for non-pre-releases.
Add banner to docs for non-pre-releases.

matthewdupre/felix,Metaswitch/calico,TrimBiggs/calico,matthewdupre/felix,neiljerram/felix,Metaswitch/calico,neiljerram/felix,TrimBiggs/calico,neiljerram/felix,neiljerram/felix