Improve comments for Caddy's TLS instructions

examples/caddy/matrix-dimension

@@ -1,4 +1,6 @@
 https://dimension.DOMAIN {
+	# These might differ if you are supplying your own certificates
+	# If you wish to use Caddy's built-in Let's Encrypt support, you can also supply an email address here
 	tls /matrix/ssl/config/live/dimension.DOMAIN/fullchain.pem /matrix/ssl/config/live/dimension.DOMAIN/privkey.pem
 
 	proxy / http://127.0.0.1:8134/ {

examples/caddy/matrix-synapse

@@ -1,5 +1,6 @@
 https://matrix.DOMAIN {
 	# If you use your own certificates, your path may differ
+	# If you wish to use Caddy's built-in Let's Encrypt support, you can also supply an email address here
 	tls /matrix/ssl/config/live/matrix.DOMAIN/fullchain.pem /matrix/ssl/config/live/matrix.DOMAIN/privkey.pem
 
 	root /matrix/static-files