Script can work with poem templates

- poemwriter.py updated: now used can generate the poem based on a
template. Template can contain both the undefined syllables chars ('-'
and '*') and words / other chars. Quite an easy way to manipulate the
poem size, to define the rhyme words or just to link it with some
meaning.

- Readme file updated.

- input.txt added as an example of the template file.