sparse_dd: document the 'experimental-reads-bypass-tapdisk' option in the config file
sparse_dd: document the 'experimental-reads-bypass-tapdisk' option in the config file

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@eu.citrix.com>

xapi-project/ocaml-vhd,djs55/ocaml-vhd