Corrected spelling in the ZFTool documentation.

The first line of the introduction starts right off with a spelling error, it bothered me so I corrected the mistake.

See House M.D. (he's usually right):
http://answers.yahoo.com/question/index?qid=20070517154920AAABFVA
Merge pull request #709 from Hubenet/patch-1

Corrected spelling in the ZFTool documentation.