Some description in the device document were inconsistent with the
source code. Also fix some syntax issues to make the sentences more
fluent.
Signed-off-by: Yi Wang <foxywang@tencent.com>
Document the reason why someone might need to use the balloon device and
detail the different parameters associated with it.
Fixes#3807
Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
