Using Vim I\'m really a fan of the visual mode that allows you to insert text before a column.
Insert some spacing after the arrows,
> one > tw
Without plugin and if you have already entered your comments without emix's solution:
:,+2 s/--/ &
This will ensure all comments are to be shifted leftwise in order to align them properly.
Then blockwise select the column to which you want to align the text, and : 100<
100<