Add README in kernel/samples/bpf/

Trying to get people to notice the XDP-tutorial, and
give many hints to use libbpf instead of this out-of-date ELF-loader.

This related to issue #34

Signed-off-by: Jesper Dangaard Brouer <[email protected]>

kernel/samples/bpf/README.rst

@@ -0,0 +1,19 @@
+eBPF and XDP samples
+====================
+
+**UPDATE**: See `XDP-tutorial`_ if you want to learn eBPF-coding,
+and not depend on kernel tree (instead it uses `libbpf`_).
+
+This directory is for prototyping BPF samples, that is intended for
+inclusion in the Linux kernel tree containing `eBPF samples`_. If you don't
+intend to send this at patches to the Linux kernel, then instead look at
+`XDP-tutorial`_ for howto integrate with `libbpf`_.
+
+**WARNING**: This directory contains its own **out-of-date** BPF ELF-loader
+(in `bpf_load.c`_).  Instead people should use `libbpf`_.
+
+
+.. _eBPF samples: https://github.com/torvalds/linux/blob/master/samples/bpf/
+.. _XDP-tutorial: https://github.com/xdp-project/xdp-tutorial
+.. _bpf_load.c: bpf_load.c
+.. _libbpf: https://github.com/libbpf/libbpf