add infrastructure help text

lib/api/infrastructure.js

@@ -38,6 +38,13 @@ module.exports = {
             "${command} infrastructure search <query>"
         ]
     },
+    getHelp: function(){
+        return [
+            "Infrastructure:",
+            "  Commands:",
+            "    search <query>   query for hosts or metrics with <query> (see http://docs.datadoghq.com/api/#search)",
+        ];
+    },
     handleCli: function(subcommand, args, callback){
         var query = args._[4];
         search(query, callback);