selftests/bpf: Document vmtest.sh dependencies

Add a list of vmtest script dependencies to make it easier for new
contributors to get going.
Signed-off-by: Evgeniy Litvinenko <evgeniyl@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210723223645.907802-1-evgeniyl@fb.com

tools/testing/selftests/bpf/README.rst

@@ -19,6 +19,13 @@ the CI. It builds the kernel (without overwriting your existing Kconfig), recomp
 bpf selftests, runs them (by default ``tools/testing/selftests/bpf/test_progs``) and
 saves the resulting output (by default in ``~/.bpf_selftests``).
 
+Script dependencies:
+- clang (preferably built from sources, https://github.com/llvm/llvm-project);
+- pahole (preferably built from sources, https://git.kernel.org/pub/scm/devel/pahole/pahole.git/);
+- qemu;
+- docutils (for ``rst2man``);
+- libcap-devel.
+
 For more information on about using the script, run:
 
 .. code-block:: console