added l3 to architecture.rst
added l3 to architecture.rst

neiljerram/felix,ocadotechnology/calico,anortef/calico,ocadotechnology/calico,nbartos/calico,matthewdupre/felix,kasisnu/calico,beddari/calico,alexhersh/calico,anortef/calico,kasisnu/calico,neiljerram/felix,neiljerram/felix,neiljerram/felix,nbartos/calico,beddari/calico,alexhersh/calico,TrimBiggs/calico,Metaswitch/calico,TrimBiggs/calico,matthewdupre/felix,Metaswitch/calico