maintainers: add ABI versioning
maintainers: add ABI versioning

Reference the new framework and policy for ABI versioning,
in the MAINTAINERS file.

Signed-off-by: Thomas Monjalon <ee2fa8b2681c737f775687e475dcbf2028a412f1@6wind.com>
Acked-by: Neil Horman <3316dc2d77df57653443c0391a5296176d6ca9c3@tuxdriver.com>

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