Add warning for a known issue in a newly added API

checkUriPermissions is a new API added in Android S to check multiple
uri permissions via single API call.
However, checkUriPermissions is not working as intended for secondary
users. The root cause has been found and the fix is merged for later
releases.

Bug: 194700183
Test: atest --user-type secondary_user CtsScopedStorageDeviceOnlyTest:android.scopedstorage.cts.device.RedactUriDeviceTest#testSharedRedactedUri_openFileForRead
Change-Id: I72db7f0b4ddf97dce14880b6341799106d711c5c