tweaked help text on default certificate authority
tweaked help text on default certificate authority

ushuz/letsencrypt,Trim/acme-dns-tiny,oittaa/acme-tiny,corokada/acme-tiny,appuio/acme-tiny,rspeed/acme-simple,corokada/acme-tiny,diafygi/acme-tiny,oittaa/acme-tiny,appuio/acme-tiny,appuio/acme-tiny