Add comments on compat files

To prevent further confusion.

Bug: 258029505
Test: manual
Change-Id: Iaa145e4480833a224b1a07fc68adb7d3e8a36e4b
diff --git a/private/compat/29.0/29.0.cil b/private/compat/29.0/29.0.cil
index 5dba020..7315687 100644
--- a/private/compat/29.0/29.0.cil
+++ b/private/compat/29.0/29.0.cil
@@ -14,6 +14,7 @@
 (type sysfs_mac_address)
 (type wificond_service)
 
+;; mapping information from ToT policy's types to 29.0 policy's types.
 (expandtypeattribute (accessibility_service_29_0) true)
 (expandtypeattribute (account_service_29_0) true)
 (expandtypeattribute (activity_service_29_0) true)