README: Change "api" to "API"
README: Change "api" to "API"

Signed-off-by: Andrea Bolognani <3ada0bee826c753786fdbba72243dfba997094cf@redhat.com>

libvirt/libvirt-go,libvirt/libvirt-go,libvirt/libvirt-go,libvirt/libvirt-go