meson: Update json-control help description

Attempt to better specify what the json-control meson option does, which
is to allow one to use YAML based fan control even when everything else
uses JSON because the json-config option was enabled.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I08531b16a707792ad79ef2dabd8320327ce7f1e4
1 file changed