Add --plot-to-board to plot command

This flag of plot command will send the plotted burndown chart to the first
card of the `Done` column.

close #134

lib/cli.rb

@@ -193,6 +193,7 @@ def burndown
   option :output, aliases: :o, desc: 'Output directory', required: false
   option 'with-fast-lane', desc: 'Plot Fast Lane with new cards bars', required: false, type: :boolean
   option 'no-tasks', desc: 'Do not plot tasks line', required: false, type: :boolean
+  option :plot_to_board, type: :boolean, desc: 'Send the plotted data to the first card of Done column'
   def plot(sprint_number)
     process_global_options options
     BurndownChart.plot(sprint_number, options)