update power management readme

modules/pwrMgmt/README.md

@@ -14,7 +14,7 @@ Given that this configuration is in the `machine/<hostname>` directory (where ho
     # other configuration files here...
   ];
 
-  customPowerManagement = {
+  pwrMgmt = {
     enable = true;
     cpuFreqGovernor = "performance";
     powertop.enable = false;
@@ -29,7 +29,7 @@ Given that this configuration is in the `machine/<hostname>` directory (where ho
     # other configuration files here...
   ];
 
-  customPowerManagement = {
+  pwrMgmt = {
     enable = true;
     cpuFreqGovernor = "powersave";
     powertop = {