Clarify server-members is server-only (#1761)

* Add a note to the CLI that only servers can run this command

* Add a callout that this is a server command

* Remove the annoying bottom margin on callouts

command/server_members.go

@@ -17,7 +17,8 @@ func (c *ServerMembersCommand) Help() string {
 	helpText := `
 Usage: nomad server-members [options]
 
-  Display a list of the known servers and their status.
+  Display a list of the known servers and their status. Only Nomad servers are
+  able to service this command.
 
 General Options:
 

website/source/assets/stylesheets/_global.scss

@@ -81,6 +81,10 @@ pre {
   text-align: center;
 }
 
+.alert p:last-child {
+  margin-bottom: 0;
+}
+
 //fixed grid below 992 to prevent smaller responsive sizes
 @media (max-width: 992px) {
   .container{

website/source/docs/commands/server-members.html.md.erb

@@ -12,6 +12,9 @@ The `server-members` command displays a list of the known servers in the cluster
 and their current status. Member information is provided by the gossip protocol,
 which is only run on server nodes.
 
+~> **Only runs on servers!** This command can only be run from the server nodes.
+Running <tt>nomad server-members</tt> from a client will result in an error.
+
 ## Usage
 
 ```