Add a note about the payloads unit-based internal facade.
Add a note about the payloads unit-based internal facade.

dimitern/juju,dooferlad/juju,voidspace/juju,gabriel-samfira/juju,davecheney/juju,alesstimec/juju,bogdanteleaga/juju,mikemccracken/juju,bac/juju,axw/juju,kat-co/juju,reedobrien/juju,macgreagoir/juju,perrito666/juju,AdamIsrael/juju,kat-co/juju,howbazaar/juju,wwitzel3/juju,voidspace/juju,makyo/juju,ericsnowcurrently/juju,gabriel-samfira/juju,bogdanteleaga/juju,perrito666/juju,marcmolla/juju,dimitern/juju,voidspace/juju,waigani/juju,waigani/juju,mjs/juju,AdamIsrael/juju,anastasiamac/juju,mjs/juju,marcmolla/juju,dooferlad/juju,bac/juju,waigani/juju,alesstimec/juju,dooferlad/juju,bogdanteleaga/juju,bz2/juju,howbazaar/juju,davecheney/juju,mjs/juju,howbazaar/juju,fwereade/juju,anastasiamac/juju,fwereade/juju,waigani/juju,AdamIsrael/juju,mjs/juju,wwitzel3/juju,frankban/juju,dooferlad/juju,howbazaar/juju,macgreagoir/juju,macgreagoir/juju,mikemccracken/juju,ericsnowcurrently/juju,axw/juju,perrito666/juju,dimitern/juju,mjs/juju,bz2/juju,makyo/juju,frankban/juju,kat-co/juju,mikemccracken/juju,dimitern/juju,davecheney/juju,ericsnowcurrently/juju,frankban/juju,gabriel-samfira/juju,mjs/juju,fwereade/juju,alesstimec/juju,reedobrien/juju,dimitern/juju,bac/juju,AdamIsrael/juju,dooferlad/juju,bz2/juju,bz2/juju,howbazaar/juju,kat-co/juju,anastasiamac/juju,bac/juju,gabriel-samfira/juju,reedobrien/juju,perrito666/juju,marcmolla/juju,ericsnowcurrently/juju,mikemccracken/juju,ericsnowcurrently/juju,perrito666/juju,fwereade/juju,marcmolla/juju,anastasiamac/juju,frankban/juju,axw/juju,mikemccracken/juju,wwitzel3/juju,anastasiamac/juju,davecheney/juju,reedobrien/juju,bogdanteleaga/juju,reedobrien/juju,makyo/juju,makyo/juju,axw/juju,marcmolla/juju,bz2/juju,kat-co/juju,gabriel-samfira/juju,mjs/juju,bac/juju,macgreagoir/juju,alesstimec/juju,axw/juju,voidspace/juju,frankban/juju,alesstimec/juju,macgreagoir/juju,wwitzel3/juju