some clarifying help docs on 'triton wait'

lib/do_wait_instance.js

@@ -87,12 +87,15 @@ function do_wait_instance(subcmd, opts, args, cb) {
 
 do_wait_instance.aliases = ['wait'];
 do_wait_instance.help = [
-    'Wait on 1 or more instances.',
+    'Wait on instances moving to given states.',
     '',
     'Usage:',
-    '       {{name}} wait <alias|id> [state]',
+    '       {{name}} wait <name|id> [<states>]',
     '',
-    '{{options}}'
+    '{{options}}',
+    'Where "states" is a comma-separated list of target instance states,',
+    'by default "running,failed". In other words, "triton wait foo0" will',
+    'wait for instance "foo0" to complete provisioning.'
 ].join('\n');
 do_wait_instance.options = [
     {