Updated config.tpl comments to include how to exclude CPU/GPUs

xmrstak/backend/amd/config.tpl

@@ -12,6 +12,9 @@ R"===(
  * [
  *	{ "index" : 0, "intensity" : 1000, "worksize" : 8, "affine_to_cpu" : false, "strided_index" : true },
  * ],
+ * If you do not wish to mine with your AMD GPU(s) then use:
+ * "gpu_threads_conf" :
+ * null,
  */
 
 "gpu_threads_conf" : [

xmrstak/backend/cpu/config.tpl

@@ -24,6 +24,9 @@ R"===(
  *      { "low_power_mode" : false, "no_prefetch" : true, "affine_to_cpu" : 0 },
  *      { "low_power_mode" : false, "no_prefetch" : true, "affine_to_cpu" : 1 },
  * ],
+ * If you do not wish to mine with your CPU(s) then use:
+ * "cpu_threads_conf" :
+ * null,
  */
 
 "cpu_threads_conf" :

xmrstak/backend/nvidia/config.tpl

@@ -26,6 +26,9 @@ R"===(
  *       "affine_to_cpu" : false, "sync_mode" : 3,
  *     },
  * ],
+ * If you do not wish to mine with your nVidia GPU(s) then use:
+ * "gpu_threads_conf" :
+ * null,
  */
 
 "gpu_threads_conf" :