Add note regarding quoting values for network.host

Values for the network.host setting can often contain a colon which is a
character that is considered special by YAML (these arise in IPv6
addresses and some of the special tags like ":ipv4"). As such, these
values need to be quoted or a YAML parser will be unhappy with
them. This commit adds a note to the docs regarding this.

docs/reference/modules/network.asciidoc

@@ -19,10 +19,12 @@ Never expose an unprotected node to the public internet.
 
 `network.host`::
 
-The node will bind to this hostname or IP address and _publish_ (advertise)
-this host to other nodes in the cluster. Accepts an IP address, hostname, a
-<<network-interface-values,special value>>, or an array of any combination
-of these.
+The node will bind to this hostname or IP address and _publish_ (advertise) this
+host to other nodes in the cluster. Accepts an IP address, hostname, a
+<<network-interface-values,special value>>, or an array of any combination of
+these. Note that any values containing a `:` (e.g., an IPv6 address or
+containing one of the <<network-interface-values,special value>>) must be quoted
+because `:` is a special character in YAML.
 +
 Defaults to `_local_`.