README: Add -s to example
README: Add -s to example

Without the -s, it simply runs in the background.  Add
-s to the example string.

Signed-off-by: Sean Cross <dd28e116ed3e781f3ae781acae9fb18383f35c2f@kosagi.com>

pfalcon/fernly,pfalcon/fernly,urjaman/fernly,mandl/fernly,mandl/fernly,urjaman/fernly,urjaman/fernly,xobs/fernly,xobs/fernly,mandl/fernly