Update README.md

Adding the definition of wit =)

README.md

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 ===
 
 Wit is a tool written in Python that adds a chosen watermark to every image in the same folder.
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+-- * --
+wit /wɪt/
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+n
+- the talent or quality of using unexpected associations between contrasting or disparate words or ideas to make a clever humorous effect
+speech or writing showing this quality
+- a person possessing, showing, or noted for such an ability, esp in repartee
+- practical intelligence (esp in the phrase have the wit to)
+- archaic mental capacity or a person possessing it