selftests/bpf: Clarify llvm dependency with btf_tag selftest

btf_tag selftest needs certain llvm versions (>= llvm14).
Make it clear in the selftests README.rst file.
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211112012651.1508549-1-yhs@fb.com

tools/testing/selftests/bpf/README.rst

@@ -204,16 +204,17 @@ __ https://reviews.llvm.org/D93563
 btf_tag test and Clang version
 ==============================
 
-The btf_tag selftest require LLVM support to recognize the btf_decl_tag attribute.
-It was introduced in `Clang 14`__.
+The btf_tag selftest requires LLVM support to recognize the btf_decl_tag and
+btf_type_tag attributes. They are introduced in `Clang 14` [0_, 1_].
 
-Without it, the btf_tag selftest will be skipped and you will observe:
+Without them, the btf_tag selftest will be skipped and you will observe:
 
 .. code-block:: console
 
   #<test_num> btf_tag:SKIP
 
-__ https://reviews.llvm.org/D111588
+.. _0: https://reviews.llvm.org/D111588
+.. _1: https://reviews.llvm.org/D111199
 
 Clang dependencies for static linking tests
 ===========================================