design: Improve and update intro paragraphs
design: Improve and update intro paragraphs

* Minor grammar and working improvements
* Update to current state of CSI in k8s, ceph-csi

Signed-off-by: John Mulligan <eda8ad33169deab44f9fe65847f99e368da6c91b@redhat.com>

rook/rook,rook/rook,rook/rook,rook/nfs,rook/rook,rook/nfs,rook/rook,rook/nfs