Merge pull request arogozhnikov#31 from KonstantinSchubert/patch-1

Fixed a typo

README.md

@@ -54,7 +54,7 @@ Libraries you'll require to make your life easier.
 * [yandex/REP](https://github.com/yandex/REP)  — python wrappers around different machine learning libraries 
     (including TMVA) + goodies, required to plot learning curves and reports after classification. Required to execute *howto*s from this repository
 * [numpy](http://www.numpy.org/)  — 'MATLAB in python', vector operation in python. 
-    Use it you need to perform any number crunching. 
+    Use it whenever you need to perform any number crunching. 
 * [theano](http://deeplearning.net/software/theano/)  — optimized vector analytical math engine in python
 * [ROOT](https://root.cern.ch/)  — main data format in high energy physics 
 * [root_numpy](http://rootpy.github.io/root_numpy/)  — python library to deal with ROOT files (without pain)