Minor fixes to CLI help messages

src/command/apply.rs

@@ -16,8 +16,12 @@ pub fn subcommand() -> App<'static, 'static> {
         .arg(Arg::with_name("parallel")
             .short("p")
             .long("parallel")
+            .value_name("LIMIT")
             .help("Parallelism limit")
-            .long_help("Set to 0 to disable parallemism limit.")
+            .long_help(r#"Limits the maximum number of hosts to be deployed in parallel.
+
+Set to 0 to disable parallemism limit.
+"#)
             .default_value("10")
             .takes_value(true)
             .validator(|s| {

src/main.rs

@@ -41,6 +41,7 @@ async fn main() {
         .arg(Arg::with_name("config")
             .short("f")
             .long("config")
+            .value_name("CONFIG")
             .help("Path to a Hive expression")
 
             // The default value is a lie (sort of)!

src/util.rs

@@ -126,9 +126,11 @@ pub fn register_selector_args<'a, 'b>(command: App<'a, 'b>) -> App<'a, 'b> {
     command
         .arg(Arg::with_name("on")
             .long("on")
-            .help("Select a list of machines")
-            .long_help(r#"The list is comma-separated and globs are supported. To match tags, prepend the filter by @.
-Valid examples:
+            .value_name("NODES")
+            .help("Node selector")
+            .long_help(r#"Select a list of nodes to deploy to.
+
+The list is comma-separated and globs are supported. To match tags, prepend the filter by @. Valid examples:
 
 - host1,host2,host3
 - edge-*