Add detailed guide for file_list_diff error

Add README.md for more details and error resolution guide for the
file_list_diff tool. Guide users to read the REAMDE.md doc with the
error message to help them fix the errors.

Bug: 411254556
Test: m out/target/product/<product>/obj/PACKAGING/system_intermediates/file_diff.timestamp
Change-Id: If2ad3ba97ad86839d777c2b509f3e823105d3d13