Add note about required let's encrypt port
Add note about required let's encrypt port

Let's Encrypt uses tls-sni to validate the certificate
on the standard https port 443. If the registry is
outwardly listening on a different port Let's Encrypt
will not issue a certificate.

Signed-off-by: Derek McGowan <e1c79a582b6629e6b39e9679f4bb964d25db4aa8@mcgstyle.net> (github: dmcgowan)

yuwaMSFT2/distribution,RichardScothern/distribution,spacexnice/distribution,jwhonce/distribution,mbentley/distribution,jwhonce/distribution,nwt/distribution,jzwlqx/distribution,sergeyfd/distribution,shyr/distribution,estesp/distribution,dobril-stanga/distribution,dobril-stanga/distribution,miminar/distribution,sergeyfd/distribution,konstruktoid/distribution,huamai-io/distribution,RichardScothern/distribution,shyr/distribution,sadlil/distribution,duglin/distribution,estesp/distribution,dmcgowan/distribution,dmcgowan/distribution,konnase/distribution,mikebrow/distribution,yuwaMSFT2/distribution,harrisonfeng/distribution,harrisonfeng/distribution,vdemeester/distribution,manoj535/distribution,miminar/distribution,mikebrow/distribution,docker/distribution,nwt/distribution,konstruktoid/distribution,manoj535/distribution,cezarsa/distribution,duglin/distribution,konnase/distribution,thaJeztah/distribution,thaJeztah/distribution,cezarsa/distribution,spacexnice/distribution,vdemeester/distribution,mbentley/distribution,huamai-io/distribution,docker/distribution,sadlil/distribution,jzwlqx/distribution