doc: improve examples.

docs/content/https/ref-acme.txt

@@ -1,5 +1,4 @@
 # Enable ACME (Let's Encrypt): automatic SSL.
---certificatesResolvers.sample.acme
 
 # Email address used for registration.
 #
@@ -35,13 +34,13 @@
 #
 # Optional (but recommended)
 #
---certificatesResolvers.sample.acme.tlsChallenge
+--certificatesResolvers.sample.acme.tlsChallenge=true
 
 # Use a HTTP-01 ACME challenge.
 #
 # Optional
 #
---certificatesResolvers.sample.acme.httpChallenge
+--certificatesResolvers.sample.acme.httpChallenge=true
 
 # EntryPoint to use for the HTTP-01 challenges.
 #
@@ -54,7 +53,7 @@
 #
 # Optional
 #
---certificatesResolvers.sample.acme.dnsChallenge
+--certificatesResolvers.sample.acme.dnsChallenge=true
 
 # DNS provider used.
 #