docs: fix: Match stated automake requirement

docs: fix: Match stated automake requirement

to the applied requirement. Previously, the README stated the minimum
required version of automake was 1.10. However, since commit 343a7a984
(Require automake >= 1.12), the configuration script (configure.ac)
actually enforced a minimum of 1.12:

AM_INIT_AUTOMAKE([1.12 foreign dist-bzip2 no-dist-gzip tar-pax ...

Change-Id: I4f9fcc3aca340e4638e93d69155c51f82247e29d
Signed-off-by: Erica Bugden <ebugden@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>