Fix demo vagrant server by making hostname resolve

website/source/intro/getting-started/cluster.html.md

@@ -33,6 +33,14 @@ server {
     # Self-elect, should be 3 or 5 for production
     bootstrap_expect = 1
 }
+
+# Advertise must be set to a non-loopback address.
+# Defaults to the resolving the local hostname.
+#advertise {
+#    http = "10.0.2.1"
+#    rpc  = "10.0.2.1"
+#    serf = "10.0.2.1"
+#}
 ```
 
 This is a fairly minimal server configuration file, but it