added data preprocessing tool

1-Introduction/5-data-preprocessing-tool/README.md

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+## Dataset 
+Dataset is of retail company that collected data from their customers wheather or not they purchased some product.
+Each row belong to different customers and includes customer name, age, salary and wheather or not they purchased some product (YES or NO).
+
+x --> freatures  (first three colums) </br>
+y --> dependent variable vector (last column)
+
+

1-Introduction/5-data-preprocessing-tool/data/retail-company.csv

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+Country,Age,Salary,Purchased
+France,44,72000,No
+Spain,27,48000,Yes
+Germany,30,54000,No
+Spain,38,61000,No
+Germany,40,,Yes
+France,35,58000,Yes
+Spain,,52000,No
+France,48,79000,Yes
+Germany,50,83000,No
+France,37,67000,Yes