selftest/bpf: Fix link in readme

The link was bad because of invalid rst; it was pointing to itself and
was rendering badly.

Signed-off-by: Andrei Matei <andreimatei1@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20201122022205.57229-1-andreimatei1@gmail.com

tools/testing/selftests/bpf/README.rst

@@ -2,7 +2,10 @@
 BPF Selftest Notes
 ==================
 General instructions on running selftests can be found in
-`Documentation/bpf/bpf_devel_QA.rst`_.
+`Documentation/bpf/bpf_devel_QA.rst`__.
+
+__ /Documentation/bpf/bpf_devel_QA.rst#q-how-to-run-bpf-selftests
+
 
 Additional information about selftest failures are
 documented here.