health: properly support charger mode.

Use charger_vendor SELinux context.

Also update readme to reflect the change.

Test: manual in offline-charging mode
Bug: 177269435
Change-Id: Icf5cd9d579b3365037e2d360fcc29b0ef4be1b15
diff --git a/health/aidl/default/android.hardware.health-service.example.rc b/health/aidl/default/android.hardware.health-service.example.rc
index dee3d11..4258890 100644
--- a/health/aidl/default/android.hardware.health-service.example.rc
+++ b/health/aidl/default/android.hardware.health-service.example.rc
@@ -7,6 +7,7 @@
 
 service vendor.charger-default /vendor/bin/hw/android.hardware.health-service.example --charger
     class charger
+    seclabel u:r:charger_vendor:s0
     user system
     group system wakelock input
     capabilities SYS_BOOT