libbpf: Improve libbpf API documentation link position

This puts the link for libbpf API documentation into the sidebar
for much easier navigation.

You can preview this change at:

  https://libbpf-test.readthedocs.io/en/latest/

Note that the link is hardcoded to the production version, so you
can see that it self references itself here for now:

  https://libbpf-test.readthedocs.io/en/latest/api.html

This will need to make its way into the libbpf mirror, before being
deployed to libbpf.readthedocs.org

Signed-off-by: Grant Seltzer <grantseltzer@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220422031050.303984-1-grantseltzer@gmail.com

Documentation/bpf/libbpf/index.rst

@@ -6,14 +6,13 @@ libbpf
 .. toctree::
    :maxdepth: 1
 
+   API Documentation <https://libbpf.readthedocs.io/en/latest/api.html>
    libbpf_naming_convention
    libbpf_build
 
 This is documentation for libbpf, a userspace library for loading and
 interacting with bpf programs.
 
-For API documentation see the `versioned API documentation site <https://libbpf.readthedocs.io/en/latest/api.html>`_.
-
 All general BPF questions, including kernel functionality, libbpf APIs and
 their application, should be sent to bpf@vger.kernel.org mailing list.
 You can `subscribe <http://vger.kernel.org/vger-lists.html#bpf>`_ to the