Update rail_naming.md

Added E3 NPU component energy.

Author: hkmsft

windows-driver-docs-pr/powermeter/rail_naming.md

@@ -23,6 +23,7 @@ Energy Estimation Engine (E3) attributes energy to software applications. If the
 | MBB or MBB_*         | mbb       |
 | DISPLAY or DISPLAY_* | display   |
 | GPU or GPU_*         | soc       |
+| NPU or NPU_*         | npu       |
 
 ## How the rails are mapped to E3 component energy