balloon: update public documentation
balloon: update public documentation

Added user recommendations in the balloon public documentation for the
case where the memory restrictions imposed on the VM through the
balloon device are broken.

Signed-off-by: George Pisaltu <084beef259e7feee20f091a1c4e2b24ee6aa34bb@amazon.com>

firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker