There seems to be little point in substituting the version number into
README (using autotools). Rename it to README.md and distribute that
verbatim (with autotools and Meson) instead.
Autotools still requires that README exists, so leave a stub README file
in place which redirects people to README.md. This can be dropped when
we drop autotools support.
Signed-off-by: Philip Withnall <withnall@endlessm.com>
