doc: Modifies keyring path in radosgw config page.
doc: Update syntax for rbd children

The docs were incorrectly usins 'rbd snap children' when the actual
command is 'rbd children'.

Signed-off-by: Travis Rhoden <trhoden@gmail.com>
Merge pull request #432 from kri5/wip-radosgw-config-doc

doc: Modifies keyring path in radosgw config page.
Merge pull request #449 from trhoden/rbd_child_doc

Reviewed-by: Josh Durgin <josh.durgin@inktank.com>