health: update readme for writing kmesg

Test: none
Bug: 77661605
Change-Id: Iea07a8361e7c23919515d8550d90d2bd329e616a
diff --git a/health/2.0/README b/health/2.0/README
index 49b2b1e..dc97d43 100644
--- a/health/2.0/README
+++ b/health/2.0/README
@@ -53,6 +53,7 @@
     class hal
     user system
     group system
+    file /dev/kmsg w
 
 5. Create device/<manufacturer>/<device>/health/HealthService.cpp: