fixed missing double -

The section about using yadtshell as a command and status information had two
incorrect examples:

  -dryrun and -full

which should have been:

  --dryrun and --full

The -dryrun was fixed by changing to the liberation serif font and adding an
additional -. The -full was already in liberation serif font and simply needed
an additional --.
Merge pull request #2 from esc/master

fixed missing double -