updated docs

docs/Trainer/SLURM Managed Cluster.md

@@ -25,6 +25,9 @@ parser.opt_list('--nb_layers', default=2, type=int, tunable=True, options=[2, 4,
 hparams = parser.parse_args()    
 ```    
     
+**NOTE** You must set ```Tunable=True``` for that argument to be considered in the permutation set. Otherwise
+test-tube will use the default value. This flag is useful when you don't want to search over an argument and
+want to use the default instead.   
      
 (2). Define the cluster options in the [SlurmCluster object](https://williamfalcon.github.io/test-tube/hpc/SlurmCluster/) (over 5 nodes and 8 gpus)