Add comments to "public.libraries.*.txt".

Folks don't know how to add public native API. Point them in the right
direction.

Bug: 63905942
Test: boots
Change-Id: I5e1f04fb852348255a2f7f87aa961948c41c47fd
diff --git a/rootdir/etc/public.libraries.android.txt b/rootdir/etc/public.libraries.android.txt
index e6c94ff..e70ed51 100644
--- a/rootdir/etc/public.libraries.android.txt
+++ b/rootdir/etc/public.libraries.android.txt
@@ -1,3 +1,4 @@
+# See https://android.googlesource.com/platform/ndk/+/master/docs/PlatformApis.md
 libandroid.so
 libc.so
 libcamera2ndk.so
diff --git a/rootdir/etc/public.libraries.wear.txt b/rootdir/etc/public.libraries.wear.txt
index 292730a..e494ee0 100644
--- a/rootdir/etc/public.libraries.wear.txt
+++ b/rootdir/etc/public.libraries.wear.txt
@@ -1,3 +1,4 @@
+# See https://android.googlesource.com/platform/ndk/+/master/docs/PlatformApis.md
 libandroid.so
 libc.so
 libcamera2ndk.so