(docs) add a new 'M5: supporting SDC image builds'
(docs) add a new 'M5: supporting SDC image builds'

numericillustration/sdc-imgapi,joyent/sdc-imgapi,numericillustration/sdc-imgapi,joyent/sdc-imgapi,numericillustration/sdc-imgapi,joyent/sdc-imgapi