Patch for jail.8 to remove references to sysinstall which is not part of Dragonfly

[Tomaž Borštnar]

Joerg Sonnenberger wrote:
Here is small patch to fix references to sysinstall which is not part of 
Dragonfly.
Commited. No thanks because this was a context diff :)
What is the proper patch format then? :)

Tomaž