[README] Some tips.

Author: Vescrity

README.md

@@ -7,3 +7,6 @@ Simple daemon to set value of CPU DMA Latency (`/dev/cpu_dma_latency`)
 ```bash
 dmald <latency_value> #(or -1 to terminate daemon)
 ```
+
+- The first process will be the daemon, and others will send signal to the daemon to change the value.  
+- You may need to be **root** or a member of **realtime**.