doc: link ABI policy to release notes
doc: link ABI policy to release notes

When moving ABI policy to guidelines, the new doc was referred
without using sphinx link.

Fixes: f1ef9794f9bd ("doc: add ABI guidelines")

Signed-off-by: Thomas Monjalon <ee2fa8b2681c737f775687e475dcbf2028a412f1@6wind.com>

john-mcnamara-intel/dpdk,venkynv/dpdk-mirror,venkynv/dpdk-mirror,mixja/dpdk,tsphillips/dpdk-fork,venkynv/dpdk-mirror,tsphillips/dpdk-fork,mixja/dpdk,tsphillips/dpdk-fork,tsphillips/dpdk-fork,mixja/dpdk,msune/dpdk,john-mcnamara-intel/dpdk,venkynv/dpdk-mirror,mixja/dpdk,msune/dpdk,msune/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,msune/dpdk