Remind the reader that they'll need to modify CTS too.

Also duplicate the warning to the other set of updatable ids.

Bug: http://b/364993041
Change-Id: I128ddeb468c1f2f872772c9f2505a29f7537eb8a
diff --git a/libcutils/include/private/android_filesystem_config.h b/libcutils/include/private/android_filesystem_config.h
index eeb0394..b0bddf5 100644
--- a/libcutils/include/private/android_filesystem_config.h
+++ b/libcutils/include/private/android_filesystem_config.h
@@ -143,7 +143,8 @@
 #define AID_PRNG_SEEDER 1092         /* PRNG seeder daemon */
 #define AID_UPROBESTATS 1093         /* uid for uprobestats */
 #define AID_CROS_EC 1094             /* uid for accessing ChromeOS EC (cros_ec) */
-/* Changes to this file must be made in AOSP, *not* in internal branches. */
+// Additions to this file must be made in AOSP, *not* in internal branches.
+// You will also need to update expect_ids() in bionic/tests/grp_pwd_test.cpp.
 
 #define AID_SHELL 2000 /* adb and debug shell user */
 #define AID_CACHE 2001 /* cache access */
@@ -158,7 +159,7 @@
 #define AID_OEM_RESERVED_START 2900
 #define AID_OEM_RESERVED_END 2999
 
-/* The 3000 series are intended for use as supplemental group id's only.
+/* The 3000 series are intended for use as supplemental group ids only.
  * They indicate special Android capabilities that the kernel is aware of. */
 #define AID_NET_BT_ADMIN 3001 /* bluetooth: create any socket */
 #define AID_NET_BT 3002       /* bluetooth: create sco, rfcomm or l2cap sockets */
@@ -172,6 +173,8 @@
 #define AID_UHID 3011         /* Allow read/write to /dev/uhid node */
 #define AID_READTRACEFS 3012  /* Allow tracefs read */
 #define AID_VIRTUALMACHINE 3013 /* Allows VMs to tune for performance*/
+// Additions to this file must be made in AOSP, *not* in internal branches.
+// You will also need to update expect_ids() in bionic/tests/grp_pwd_test.cpp.
 
 /* The range 5000-5999 is also reserved for vendor partition. */
 #define AID_OEM_RESERVED_2_START 5000