samples/bpf: Add note to README about the XDP utilities moved to xdp-tools

To help users find the XDP utilities, add a note to the README about the
new location and the conversion documentation in the commit messages.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/r/20230824102255.1561885-8-toke@redhat.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: tohojo

samples/bpf/README.rst

@@ -4,6 +4,12 @@ eBPF sample programs
 This directory contains a test stubs, verifier test-suite and examples
 for using eBPF. The examples use libbpf from tools/lib/bpf.
 
+Note that the XDP-specific samples have been removed from this directory and
+moved to the xdp-tools repository: https://github.com/xdp-project/xdp-tools
+See the commit messages removing each tool from this directory for how to
+convert specific command invocations between the old samples and the utilities
+in xdp-tools.
+
 Build dependencies
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