Make a statement in README that we would never charge to
use Fastsocket

Signed-off-by: Xiaofeng Lin <jerrylin.lxf@gmail.com>
Fix Bug: It is not a good idea to apply DIRECT-TCP to listen
socket and make established sockets inherit dst cache from
their listen socket. Because that would result all established
sockets have the same dst cache even these sockets could
have different remote IP addresses.

Signed-off-by: Xiaofeng Lin <jerrylin.lxf@gmail.com>