Features/cygnus acceptance test

append new comment in readme:
```
Some examples:
   lettucetdaf                                   -- run all features
   lettucetdaf -ft ckan_row.feature              -- run only one feature
   lettucetdaf -tg test -ft ckan_row.feature     -- run scenarios tagged with "test" in a feature
   lettucetdaf -tg=-skip -ft ckan_row.feature    -- run all scenarios except tagged with "skip" in a feature
```