Fix the 'managing daemons' doc's example for launching daemons in a
way suitable for multiple web servers. Separate the '--no-discovery'
argument with '--', otherwise it doesn't appear to be understood.

Attempt to launch daemon in various ways, make sure to include
ways that are expected to fail, otherwise it may not be doing what
we expect.

phd launch PhabricatorRepositoryPullLocalDaemon --no-discovery
.. errors in daemon log 'unrecognised argument' ..
phd launch PhabricatorRepositoryPullLocalDaemon -- --not-an-arg
.. errors in daemon log 'unrecognised argument' ..
phd launch PhabricatorRepositoryPullLocalDaemon -- --no-discovery
.. no errors in daemon log ..