Add -A tasks option in all command examples, to avoid confusion

Signed-off-by: Balthazar Rouberol <balthazar.rouberol@mapado.com>
Replace the '-A tasks' option by '-A proj'

As asked in https://github.com/mher/flower/pull/223#issuecomment-43326871
Signed-off-by: Balthazar Rouberol <balthazar.rouberol@mapado.com>
Merge pull request #223 from brouberol/master

Add -A tasks option in all command examples, to avoid confusion