Note added on string concatenation

Besides the **join()** function and the **+** operator for concatenation , there is also this **%** formatting operator to merge the pre-determined number of strings. However, [What's new in Python 3](http://docs.python.org/release/3.0.1/whatsnew/3.0.html#pep-3101-a-new-approach-to-string-formatting) tells that this will be replaced by the **format()** function in the later versions. 

I added a small note about this change to keep the guys informed.